Antiviral nucleoside derivatives

ABSTRACT

The present invention relates to nucleoside derivatives for the treatment of Hepatitis C viral infections including compounds of formula I, pharmaceutical compositions comprising these compounds and methods for treatment or prophylaxis of Hepatitis C Virus mediated diseases employing said compounds in monotherapy or in combination therapy. The present invention further provides a process for preparing 1′,3′,4′-triacyl pyrimidine nucleoside from a N, 1′,3′,4′-tetraacylpyrimidine nucleoside

CROSS REFERENCE TO PRIOR APPLICATIONS

[0001] This application claims benefit under Title 35 U.S.C. 119(e) ofU.S. Provisional Application No. 60/427,447, filed Nov. 19, 2002 andU.S. Pat. No. 60/483,970, filed Jul. 1, 2003, which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

[0002] The invention relates to the field of antiviral therapy and inparticular to nucleoside derivatives for treating Hepatitis C Virus(HCV) mediated diseases. The invention provides novel chemicalcompounds, pharmaceutical compositions comprising these compounds,methods for treatment or prophylaxis of HCV mediated diseases employingsaid compounds in monotherapy or in combination therapy.

BACKGROUND OF THE INVENTION

[0003] The invention relates to nucleoside derivatives as inhibitors ofHCV replicon RNA replication. In particular, the invention is concernedwith the use of pyrimidine nucleoside compounds as inhibitors ofsubgenomic HCV RNA replication and pharmaceutical compositionscontaining such compounds.

[0004] Hepatitis C virus is the leading cause of chronic liver diseasethroughout the world. Patients infected with HCV are at risk ofdeveloping cirrhosis of the liver and subsequent hepatocellularcarcinoma and hence HCV is the major indication for livertransplantation. Only two approved therapies are currently available forthe treatment of HCV infection (R. G. Gish, Sem. Liver. Dis., 199919:5). These are interferon-α monotherapy and, more recently,combination therapy of the nucleoside analogue, ribavirin (Virazole),with interferon-α.

[0005] Many of the drugs approved for the treatment of viral infectionsare nucleosides or nucleoside analogues and most of these nucleosideanalogue drugs are converted into the corresponding triphosphate invivo. The triphosphates inhibit viral polymerase enzymes which haltsviral replication. This conversion to the triphosphate is commonlymediated by cellular kinases and therefore the direct evaluation ofnucleosides as inhibitors of HCV replication is only convenientlycarried out using a cell-based assay. For HCV the availability of a truecell-based viral replication assay or animal model of infection islacking.

[0006] Hepatitis C virus belongs to the family of Flaviridae. It is anRNA virus, the RNA genome encoding a large polyprotein that afterprocessing produces the necessary replication machinery to ensuresynthesis of progeny RNA. It is believed that most of the non-structuralproteins encoded by the HCV RNA genome are involved in RNA replication.Lohmann et al. [V. Lohmann et al., Science, 1999, 285:110-113] havedescribed the construction of a Human Hepatoma (Huh7) cell line in whichsubgenomic HCV RNA molecules have been introduced and shown to replicatewith high efficiency. It is believed that the mechanism of RNAreplication in these cell lines is identical to the replication of thefull length HCV RNA genome in infected hepatocytes. The subgenomic HCVcDNA clones used for the isolation of these cell lines have formed thebasis for the development of a cell-based assay for identifyingnucleoside analogue inhibitors of HCV replication.

[0007] U.S. application Ser. No. 10/167,106 filed Jun. 11, 2002 entitled“4′-Substituted Nucleoside Derivatives as Inhibitors of HCV RNAReplication”, discloses compounds related to the present invention.

SUMMARY OF THE INVENTION

[0008] Nucleoside derivatives frequently exhibit high levels ofbiological activity; however, their practical utility is often limitedby suboptimal physical properties and poor pharmacokinetics. The presentinvention relates to chemical derivatives of 4′-substituted nucleosideswith improved physiochemical and pharmacokinetic properties. Thesederivatives more efficiently permeate the intestinal mucosa whereupon avariety of enzymes present in the cytoplasm, blood, or serum convert thederivative to the non-derivatized nucleoside. These “pronucleotides” canimprove the properties such as activity, bioavailability or stability ofthe parent nucleotide. Administration of compounds of formula I tomammals infected by HCV inhibits subgenomic HCV replication in ahepatoma cell line.

[0009] wherein:

[0010] R¹ and R² are independently selected from the group consisting ofhydrogen, COR⁵, C(═O)OR⁵, C(═O)SR⁵, C(═O)NHR⁵ and COCH(R⁶)NHR⁷;

[0011] R³ and R⁴ independently of the other are selected from the groupconsisting of hydrogen, COR⁵, CO₂R⁵ and COCH(R⁶)NHR⁷, or R³ and R⁴ takentogether are selected from the group consisting of CH₂, C(CH₃)₂ andCHPh;

[0012] R⁵ is independently selected from the group consisting ofC₁₋₁₈unbranched or branched alkyl, C₁₋₁₈ unbranched or branched alkenyl,C₁₋₁₈ unbranched or branched alkynyl, C₁₋₁₈ lower haloalkyl, C₃₋₈cycloalkyl, alkyl substituted C₃₋₈ cycloalkyl, phenyl optionallyindependently substituted with one to three substituents selected fromthe group consisting of halo, lower alkyl, lower alkoxy, lowerthioalkyl, lower alkyl sulfinyl, lower alkyl sulfonyl, nitro, and cyano,CH₂Ph wherein in phenyl ring is optionally substituted as describedabove and CH₂OPh wherein in phenyl ring is optionally substituted asdescribed above;

[0013] R⁶ is selected from the group consisting of the side chains ofnaturally occurring amino acids and C₁₋₅ unbranched or branched alkyl;

[0014] R⁷ is selected from the group consisting of hydrogen, R⁵OCO, and;hydrates, solvates, clathrates and acid addition salts thereof; with theproviso that at least one of R¹, R², R³, or R⁴ is other than hydrogen.

[0015] The invention also provides methods of treating diseases mediatedby Hepatitis C virus by administering a compound of formula I. Thecompound can be administered alone or in combination with an immunesystem modulator, an antiviral agent, or an anti-inflammatory agent. Theinvention further includes compositions for the treatment of treatingdiseases mediated by Hepatitis C virus by administering atherapeutically effective amount of a compound of formula I.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Compounds of the present invention are pro-drugs or bioprecursorsof the parent nucleoside and are converted in vivo to the compound offormula I wherein R¹, R², R³, and R⁴ are hydrogen. Pro-drugs includeacyl derivatives, amino acid esters, alkoxycarbonyl, aryloxycarbonyl,thioalkylcarbonyl and arylthiocarbonyl nucleoside or pharmaceuticallyacceptable salts thereof.

[0017] One embodiment of the present invention is a nucleosidederivative according to formula I wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷are independently selected from the groups defined hereinabove with theproviso that at least one of R¹, R², R³, or R⁴ is other than hydrogen.

[0018] In another embodiment of the present invention there is provideda compound according to formula I wherein R¹, R², R³, and R⁴ each areindependently COR⁵, C(═O)OR⁵ or C(═O)SR⁵ and each R⁵ is independentlyselected from the group consisting of C₁₋₁₈ unbranched or branched loweralkyl, phenyl and CH₂OPh.

[0019] In another embodiment of the present invention there is provideda compound according to formula I wherein R¹, R², R³, and R⁴ are COR⁵and each R⁵is independently selected from the group consisting of C₁₋₁₈unbranched or branched lower alkyl, phenyl and CH₂OPh.

[0020] In another embodiment of the present invention there is provideda compound according to formula I wherein R¹ is COR⁵, C(═O)OR⁵, C(═O)SR⁵or COCH(R⁶)NHR⁷; R², R³ and R⁴ are hydrogen; and, R⁵ or R⁶ and R⁷ are asdefined hereinabove.

[0021] In another embodiment of the present invention there is provideda compound according to formula I wherein R¹ is COR⁵, C(═O)OR⁵, C(═O)SR⁵or COCH(R⁶)NHR⁷; R², R³ and R⁴ are hydrogen; R⁵ selected from a groupconsisting of C₁₋₁₈ unbranched or branched lower alkyl, C₃₋₈ cycloalkyl,phenyl and CH₂OPh or R⁶ is selected from the group consisting of C₁₋₅unbranched or branched alkyl and the side chain of a naturally occurringamino acid and R⁷ is as defined hereinabove.

[0022] In another embodiment of the present invention there is provideda compound according to formula I wherein R² is selected from the groupconsisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; R¹, R³ and R⁴are hydrogen; and R⁵ or R⁶ and R⁷ are as defined hereinabove.

[0023] In another embodiment of the present invention there is provideda compound according to formula I wherein R² is selected from the groupconsisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; R¹, R³ and R⁴are hydrogen; R⁵is selected from the group consisting of is C₁₋₁₈unbranched or branched alkyl, C₃₋₈ cycloalkyl and phenyl or R⁶ is C₁₋₅unbranched or branched alkyl or the side chain of a naturally occurringamino acid and R⁷ are as defined hereinabove.

[0024] In another embodiment of the present invention there is provideda compound according to formula I wherein R² is COCH(R⁶)NH₂; R¹, R³, R⁴and R⁷ are hydrogen; and, R⁶ is selected from the group consisting ofC₁₋₅ unbranched or branched alkyl or CH₂Ph.

[0025] In another embodiment of the present invention there is provideda compound according to formula I wherein R¹ and R² are independentlyselected from the group consisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ andCOCH(R⁶)NHR⁷; R³ and R⁴ are hydrogen; and, R⁵ and/or R⁶ and R⁷ areindependently selected from the group defined hereinabove.

[0026] In another embodiment of the present invention there is provideda compound according to formula I wherein R¹ is hydrogen; R², R³ and R⁴are selected from the group consisting of COR⁵, C(═O)OR⁵ or C(═O)SR⁵;and R⁵ is independently selected from the group defined hereinabove.

[0027] In another embodiment of the present invention there is provideda compound wherein R¹ is hydrogen; R² is COR⁵, C(═O)OR⁵, C(═O)SR⁵ orCOCH(R⁶)NHR⁷; R³ and R⁴ taken together are selected from the groupconsisting of CH₂, C(CH₃)₂ and CHPh; and, R⁵ or R⁶ and R⁷ areindependently selected from the group hereinabove.

[0028] In another embodiment of the present invention there is provideda compound according to formula I wherein R¹ and R² are hydrogen; R³ andR⁴ taken independently are selected from the group consisting of COR⁵,C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; and, R⁵ or R⁶ and R⁷ areindependently selected from the group hereinabove.

[0029] In another embodiment of the present invention there is provideda compound according to formula 1 wherein R¹ and R² are selected fromthe group consisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; R³and R⁴ taken together are selected from the group consisting of CH₂,C(CH₃)₂ and CHPh; R⁷ is hydrogen or C(═O)OR⁵; and R⁵ and/or R⁶ areindependently selected from the group defined hereinabove.

[0030] In another embodiment of the present invention there is provideda compound selected from the group consisting of isobutyric acid(2R,3S,4R,5R)-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-4-isobutyryloxy-2-isobutyryloxymethyl-tetrahydro-furan-3-ylester;(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-propionyloxy-5-propionyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride;(S)-1-[(3R,4S,5R)-5-Azido-3,4-bis-pentanoyloxy-5-pentanoyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride;(S)-1-[(3R,4S,5R)-5Azido-3,4-dihydroxy-5-(4-methyl-benzoyloxymethyl)-tetrahydro-furan-2-yl]-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride;(S)-1-((3R,4S,5R)-5-azido-3,4-bis-hexanoyloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;methanesulfonate;(S)-1-((3R,4S,5R)-5-azido-5-hydroxymethyl-3,4-bis-pentanoyloxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;trifluoro-acetate; Tetradecanoic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethylester;(S)-1-((3R,4S,5R)-5-azido-3,4-bis-butyryloxy-5-hydroxymethyl-tetrahydro)-furan-2yl)-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;trifluoro-acetate; and,(S)-1-((3R,4S,5R)-5-Azido-5-decyloxycarbonyloxymethyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;trifluoro-acetate.

[0031] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of anucleoside derivatives according to formula I wherein R¹, R², R³, R⁴,R⁵, R⁶ and R⁷ are defined hereinabove.

[0032] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R¹, R², R³, or R⁴ are eachindependently selected from the group consisting of COR⁵, C(═O)OR⁵ andC(═O)SR⁵ and R⁵ are independently selected from the group definedhereinabove.

[0033] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R¹, R², R³, or R⁴ are each COR⁵and each R⁵ is independently selected from the group consisting of C₁₋₁₈unbranched or branched alkyl, phenyl and CH₂OPh.

[0034] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R¹ is selected from the groupconsisting of COR⁵, CO₂R⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; R², R³, and R⁴ areeach hydrogen; and R⁵ or R⁶ and R⁷ are as defined hereinabove.

[0035] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R¹ is selected from the groupconsisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; R², R³, and R⁴are each hydrogen; R⁵ is selected from a group consisting of C₁₋₁₈unbranched or branched lower alkyl, C₃₋₈ cycloalkyl, phenyl and CH₂OPh,or R⁶ is selected from the group consisting of C₁₋₅ unbranched orbranched alkyl and the side chain of a naturally occurring amino acidand R⁷ is hydrogen.

[0036] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R² is selected from the groupconsisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; R¹, R³ and R⁴are hydrogen; and, R⁵ or R⁶ and R⁷ are as defined hereinabove.

[0037] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of aaccording to formula I wherein R² is selected from the group consistingof COR⁵, CO₂R⁵, and COCH(R⁶)NHR⁷; R′, R³ and R⁴ are hydrogen; R⁵ isselected from a group consisting of C₁₋₁₈ unbranched or branched alkyl,C₃₋₈ cycloalkyl, phenyl and CH₂OPh or R⁶ is C₁₋₅ unbranched or branchedalkyl or the side chain of a naturally occurring amino acid and R⁷ishydrogen.

[0038] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R² is COCH(R⁶)NHR⁷; R¹, R³ andR⁴ are hydrogen; R⁶ is selected form the group consisting of C₁₋₅unbranched or branched alkyl and CH₂Ph; and, R⁷is hydrogen.

[0039] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R³ and R⁴ are hydrogen; and, R¹,R², R⁵, R⁶ and R⁷ are independently selected from the groups definedhereinabove.

[0040] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R¹ is hydrogen; R², R³ and R⁴are independently selected from the group consisting of COR⁵, C(═O)OR⁵and C(═O)SR⁵ and, each R⁵ is independently selected from the groupdefined hereinabove.

[0041] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R¹ is hydrogen; R³ and R⁴, takentogether, are selected from the group consisting of CH₂, C(CH₃)₂ andCHPh; R², R⁵or R⁶ and R⁷ are as defined hereinabove.

[0042] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R¹ and R² are hydrogen; R³, R⁴,R⁵ and/or R⁶ and R⁷ are independently selected from the group definedhereinabove.

[0043] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I wherein R³ and R⁴ taken together areselected from the group consisting of CH₂, C(CH₃)₂ and CHPh; R¹, R², R⁵and/or R⁶ and R⁷ are independently selected from the group definedhereinabove.

[0044] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷are as defined hereinabove, in a dose between 1 and 100 mg/kg of bodyweight per day.

[0045] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a human in need thereof a therapeutically effective quantity of acompound according to formula I, wherein R¹ to R⁷ are as definedhereinabove.

[0046] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷are as defined hereinabove, in combination with at least one immunesystem modulator and/or antiviral agent that inhibits replication ofHCV.

[0047] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷are as defined hereinabove, in combination with at least one immunesystem modulator.

[0048] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷are as defined hereinabove, in combination with an interferon,interleukin, tumor necrosis factor, colony stimulating factor or ananti-inflammatory agent.

[0049] In another embodiment of the present invention there is provideda method for treating diseases mediated by HCV comprising administeringto a mammal in need thereof a therapeutically effective quantity of acompound according to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷are as defined hereinabove, in combination an interferon.

[0050] In another embodiment of the present invention is a method fortreating diseases mediated by HCV comprising administering to a mammalin need thereof a therapeutically effective quantity of a compoundaccording to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷ are asdefined hereinabove, in combination with interferon-α or a chemicallyderivatized interferon.

[0051] In another embodiment of the present invention is a method fortreating diseases mediated by HCV comprising administering to a mammalin need thereof a therapeutically effective quantity of a compoundaccording to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷ are asdefined hereinabove, in combination with at least one other anti-viralagent.

[0052] In another embodiment of the present invention is a method fortreating diseases mediated by HCV comprising administering to a mammalin need thereof a therapeutically effective quantity of a compoundaccording to formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ and R⁷ are asdefined hereinabove, in combination with at least one HCV proteaseinhibitor, HCV polymerase inhibitor, HCV helicase inhibitor, HCV primaseinhibitor, HCV integrase inhibitor or HCV fusion inhibitor..

[0053] In another embodiment of the present invention is apharmaceutical composition comprising a therapeutically effectivequantity of a compound of formula I, wherein R¹, R², R³, R⁴, R⁵, R⁶ andR⁷are as defined hereinabove, in combination with one or morepharmaceutically acceptable carrier, diluent or excipient with theproviso that at least one of R¹, R², R³, or R⁴ is other than hydrogen.

[0054] In another embodiment of the present invention there is provideda process for converting an N-acyl cytidine compound IVa to a cytidinecompound IVb by selective cleavage of an N-acyl moiety from

[0055] IVa wherein R is identical to R¹ as defined hereinabove; and R⁵R⁶ and R⁷ are as defined hereinabove, said process comprising contactinga solution of said N-acyl pyrimidine nucleoside with ZnBr₂ in a proticsolvent RaOH wherein Ra is hydrogen or C₁₋₄ alkyl.

[0056] In another embodiment of the present invention there is provideda process for converting IVa to IVb wherein R is identical to R¹ asdefined hereinabove; and R⁵ R⁶ and R⁷ are as defined hereinabove, saidprocess comprising contacting a solution of said N-acyl pyrimidinenucleoside with ZnBr₂ in methanol and optimally with an aprotic organicsolvent.

DEFINITIONS

[0057] The phrase “a” or “an” entity as used herein refers to one ormore of that entity; for example, a compound refers to one or morecompounds or at least one compound. As such, the terms “a” (or “an”),“one or more”, and “at least one” can be used interchangeably herein.

[0058] The phrase “as defined hereinabove” refers to the firstdefinition for each group as provided in the Summary of the Invention.

[0059] The terms “optional” or “optionally” as used herein means that adescribed event or circumstance may or may not occur, and that thedescription includes instances where said event or circumstance occursand instances in which it does not. For example, “optionally substitutedphenyl” means that the phenyl may or may not be substituted and that thedescription includes both unsubstituted phenyl and phenyl wherein thereis substitution.

[0060] Compounds of the present invention may have asymmetric centerslocated on the side chain of a carboxylic ester, amide or carbonatemoiety that produce diastereomers when linked to the nucleoside. Allstereoisomers on the side chain of the compounds of the instantinvention are contemplated, either in admixture or in pure orsubstantially pure form. The definition of the compounds according tothe invention embraces all possible stereoisomers and their mixtures. Italso embraces the racemic forms as well as the isolated optical isomers.The racemic forms can be resolved by physical methods, such as, forexample, fractional crystallization, separation or crystallization ofdiastereomeric derivatives or separation by chiral columnchromatography. The individual optical isomers can be obtained from theracemates by conventional methods, such as, for example, salt formationwith an optically active acid followed by crystallization.

[0061] All configurational isomers of compounds of the present inventionare contemplated, either in admixture or in pure or substantially pureform. The definition of compounds of the present invention embraces bothcis and trans isomers of cycloalkyl rings.

[0062] The term “alkyl” as used herein denotes an unbranched or branchedchain hydrocarbon residue containing 1 to 18 carbon atoms. The term“lower alkyl” denotes an unbranched or branched chain hydrocarbonresidue containing 1 to 6 carbon atoms. Representative lower alkylgroups include methyl, ethyl, propyl, i-propyl, n-butyl, i-butyl,t-butyl or pentyl.

[0063] The term “haloalkyl” as used herein denotes an unbranched orbranched chain alkyl group as defined above wherein 1, 2, 3 or morehydrogen atoms are substituted by a halogen. Examples are1-fluoromethyl, 1-chloromethyl, 1-bromomethyl, 1-iodomethyl,trifluoromethyl, trichloromethyl, tribromomethyl, triiodomethyl,1-fluoroethyl, 1-chloroethyl, 1-bromoethyl, 1-iodoethyl, 2-fluoroethyl,2-chloroethyl, 2-bromoethyl, 2-iodoethyl, 2,2-dichloroethyl,3-bromopropyl or 2,2,2-trifluoroethyl.

[0064] The term “cycloalkyl” as used herein denotes a saturatedcarbocyclic ring containing 3 to 8 carbon atoms, i.e. cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl or cyclooctyl.

[0065] The term “alkenyl” as used herein denotes an unsubstituted [orsubstituted] hydrocarbon chain radical having from 2 to 18 carbon atoms,preferably from 2 to 4 carbon atoms, and having one or two olefinicdouble bonds, preferably one olefinic double bond. Examples are vinyl,1-propenyl, 2-propenyl (allyl) or 2-butenyl (crotyl).

[0066] The term “alkynyl” as used herein denotes an unsubstitutedhydrocarbon chain radical having from 2 to 18 carbon atoms, [preferably2 to 4 carbon atoms], and having one or where possible two triplebonds[, preferably one triple bond]. Examples are ethynyl, 1-propynyl,2-propynyl, 1-butynyl, 2-butynyl or 3-butynyl.

[0067] The term “alkoxy” as used herein denotes an unsubstitutedunbranched or branched chain alkyloxy group wherein the “alkyl” portionis as defined above such as methoxy, ethoxy, n-propyloxy, i-propyloxy,n-butyloxy, i-butyloxy, t-butyloxy, pentyloxy, hexyloxy, heptyloxyincluding their isomers. “Lower alkoxy” as used herein denotes an alkoxygroup with a “lower alkyl” group as previously defined.

[0068] The term “alkylthio” or “thioalkyl” as used herein denotes aunbranched or branched chain (alkyl)S-group wherein the “alkyl” portionis as defined above. Examples are methylthio, ethylthio, n-propylthio,i-propylthio, n-butylthio, i-butylthio or t-butylthio.

[0069] The term “alkoxyalkyl” as used herein denotes an alkoxy group asdefined above which is bonded to an alkyl group as defined above.Examples are methoxymethyl, methoxyethyl, methoxypropyl, ethoxymethyl,ethoxyethyl, ethoxypropyl, propyloxypropyl, methoxybutyl, ethoxybutyl,propyloxybutyl, butyloxybutyl, t-butyloxybutyl, methoxypentyl,ethoxypentyl, and propyloxypentyl including their isomers.

[0070] The term “hydroxyalkyl” as used herein denotes a unbranched orbranched chain alkyl group as defined above wherein 1, 2, 3 or morehydrogen atoms are substituted by a hydroxy group. Examples arehydroxymethyl, 1-hydroxyethyl, 2-hydroxyethyl, 1-hydroxypropyl,2-hydroxypropyl, 3-hydroxypropyl, hydroxyisopropyl, hydroxybutyl and thelike.

[0071] The term “aryl” as used herein denotes an optionally substitutedmonocyclic or polycyclic-aromatic group comprising carbon and hydrogenatoms. Examples of suitable aryl groups include, but are not limited to,phenyl and naphthyl (e. g. 1-naphthyl or 2-naphthyl). Suitablesubstituents for aryl are selected from the group consisting of alkyl,alkenyl, alkynyl, aryloxy, cycloalkyl, acyl, acylamino, alkoxy, amino,alkylamino, dialkylamino, halogen, haloalkyl, hydroxy, nitro and cyano.

[0072] The term “acyl” (“alkylcarbonyl”) as used herein denotes a groupof formula C(═O)R wherein R is hydrogen, unbranched or branched alkylcontaining 1 to 7 carbon atoms or a phenyl group.

[0073] The terms “alkoxycarbonyl” and “aryloxycarbonyl” as used hereindenotes a group of formula—C(═O)OR wherein R is alkyl or arylrespectively and alkyl and aryl are as defined herein.

[0074] The terms “thioalkylcarbonyl” and “arylthiocarbonyl” as usedherein denotes a group of formula—C(═O)SR wherein R is alkyl or arylrespectively and alkyl and aryl are as defined herein

[0075] The term halogen stands for fluorine, chlorine, bromine oriodine, preferably fluorine, chlorine, bromine.

[0076] The term “amino acid” as used herein refers to naturallyoccurring amino acids, as well as to optical isomers (enantiomers anddiastereomers), synthetic analogs and derivatives thereof. α-Amino acidscomprise a carbon atom bonded to a carboxyl group, an amino group, ahydrogen atom and a unique “side chain” group. The term “naturallyoccurring amino acids” means the L-isomers of the naturally occurringamino acids. The naturally occurring amino acids are glycine, alanine,valine, leucine, isoleucine, serine, methionine, threonine,phenylalanine, tyrosine, tryptophan, cysteine, proline, histidine,aspartic acid, asparagine, glutamic acid, glutamine, γ-carboxyglutamicacid, arginine, ornithine and lysine. The side chains of naturallyoccurring amino acids include: hydrogen, methyl, iso-propyl, iso-butyl,sec-butyl, —CH₂OH, —CH(OH)CH₃, —CH₂SH, —CH₂CH₂SMe, —(CH₂)_(p)COR whereinR is —OH or —NH₂ and p is 1 or 2, —(CH₂)_(q)—NH₂ where q is 3 or 4,—(CH₂)₃—NHC(═NH)NH₂, —CH₂C₆H₅, —CH₂-p—C₆H4—H, (3-indolinyl)methylene,(4-imidazolyl)methylene.

[0077] The term “acylating agent” as used herein refers to either ananhydride, acyl halide or other activated derivative of a carboxylicacid . The term “anhydride” as used herein refers to compounds of thegeneral structure RC(O)—O—C(O)R wherein is as defined in the previousparagraph. The term “acyl halide” as used herein refers to the groupRC(O)X wherein X is bromo or chloro. The term “activated derivative” ofa compound as used herein refers to a transient reactive form of theoriginal compound which renders the compound active in a desiredchemical reaction, in which the original compound is only moderatelyreactive or non-reactive. Activation is achieved by formation of aderivative or a chemical grouping within the molecule with a higher freeenergy content than that of the original compound, which renders theactivated form more susceptible to react with another reagent. In thecontext of the present invention activation of the carboxy group is ofparticular importance. The term acylating agent as used herein furtherincludes reagents that produce carbonates (—OC(═O)OR⁵, carbamates(—NHC(═O)OR⁵), thiocarbonate(—OC(═O)SR⁵), and thiocarbamate(—NHC(═O)SR⁵), derivatives such as alkoxychlorocarbonates, R⁵OC(═O)Cl,and alkylthiochlorocarbonates, R⁵SC(═O)Cl, wherein R⁵ is as definedhereinabove.

[0078] The term “protecting group” as used herein means a chemical groupthat (a) preserves a reactive group from participating in an undesirablechemical reaction; and (b) can be easily removed after protection of thereactive group is no longer required. For example, the trialkylsilyl isa protecting group for a primary hydroxyl function and an acetonide is aprotecting group for a vicinal diol.

[0079] In the pictorial representation of the compounds given throughoutthis application, a thickened tapered line (

) indicates a substituent which is above the plane of the ring to whichthe asymmetric carbon belongs and a dotted line (

) indicates a substituent which is below the plane of the ring to whichthe asymmetric carbon belongs.

[0080] The term “combination” as used herein in reference inadministering a plurality of drugs in a therapeutic regimen byconcurrent or sequential administration of the drugs at the same time orat different times.

[0081] The term “chemically-derivatized interferon” as used hereinrefers to an interferon molecule covalently linked to a polymer whichalters the physical and/or pharmacokinetic properties of the interferon.A non-limiting list of such polymers include polyalkylene oxidehomopolymers such as polyethylene glycol (PEG) or polypropylene glycol(PPG), polyoxyethylenated polyols, copolymers thereof and blockcopolymers thereof, provided that the water solubility of the blockcopolymers is maintained. One skilled in the art will be aware ofnumerous approaches to linking the polymer and interferon (for example,see A. Kozlowski and J. M. Harris J. Control. Release 200172(1-3):217-24). A non-limiting list of chemically derivatized IFNαcontemplated in the present patent include peginterferon-α-2a (PEGASYS®)and peginterferon-α-2b (PEGINTRON®).

[0082] Compounds of formula I exhibit tautomerism. Tautomeric compoundscan exist as two or more interconvertable species. In many cases theseentities result from the shift a covalently bonded hydrogen atom shiftbetween two atoms. Tautomeric compounds exist in equilibrium with eachother, so that attempts to isolate the individual tautomers usuallyproduce a mixture having chemical and physical properties consistentwith a mixture of compounds. The position of the equilibrium isdependent on chemical features within the molecule. For example, in manyaliphatic aldehydes and ketones, such as acetaldehyde, the keto formpredominates while; in phenols, the enol form predominates. The mostcommon type of tautomerism is that involving carbonyl, (or keto)compounds and vinyl alcohols (or enols which arise from a hydrogen atomshift between the carbon and oxygen atoms and a concomitant shift in theposition of the double bond. The present invention includes lactamswhich can exist as amide or hydroxy substituted heterocyclic forms.

[0083] Compounds of formula I which are basic can form pharmaceuticallyacceptable salts with inorganic acids such as hydrohalic acids (e.g.hydrochloric acid and hydrobromic acid), sulphuric acid, nitric acid andphosphoric acid, and the like, and with organic acids (e.g. with aceticacid, tartaric acid, succinic acid, fumaric acid, maleic acid, malicacid, salicylic acid, citric acid, methanesulphonic acid and p-toluenesulphonic acid, and the like). The formation and isolation of such saltscan be carried out according to methods known in the art.

[0084] The term “solvate” as used herein means a compound of theinvention or a salt, thereof, that further includes a stoichiometric ornon-stoichiometric amount of a solvent bound by non-covalentintermolecular forces. Preferred solvents are volatile, non-toxic,and/or acceptable for administration to humans in trace amounts.

[0085] The term “hydrate” as used herein means a compound of theinvention or a salt thereof, that further includes a stoichiometric ornon-stoichiometric amount of water bound by non-covalent intermolecularforces.

[0086] The term “clathrate” as used herein means a compound of theinvention or a salt thereof in the form of a crystal lattice thatcontains spaces (e,g., channels) that have a guest molecule (e,g.), asolvent or water) trapped within.

COMPOUNDS AND PREPARATION

[0087] In general, the nomenclature used in this Application is based onAUTONOM™ v.4.0, a Beilstein Institute computerized system for thegeneration of IUPAC systematic nomenclature.

[0088] Examples of representative compounds within the scope of theinvention are provided in the following table. These examples andpreparations are provided to enable those skilled in the art to moreclearly understand and to practice the present invention. They shouldnot be considered as limiting the scope of the invention, but merely asbeing illustrative and representative thereof. The compounds of formulaI may be prepared by various methods known in the art of organicchemistry. TABLE 1

Mass Spectrum Cpd No. R¹ R² R³ R⁴ Method (M + H)+ Melting Point  1 MeCOMeCO MeCO MeCO A 453 77.0-80.1  2 EtCO EtCO EtCO EtCO A 508(M)⁺  3n-PrCO n-PrCO n-PrCO n-PrCO A 564(M)⁺  4 i-BuCO i-BuCO i-BuCO i-BuCO A621  5 t-BuCO t-BuCO t-BuCO t-BuCO A 621 67.4-80.0  6 PhCO PhCO PhCOPhCO A 700(M)⁺ 106.9-116.1  7 PhOCH₂CO PhOCH₂CO PhOCH₂CO PhOCH₂CO A 821—  8 t-BuOCO H H H B 385 80.0-83.5  9 MeCO H H H B 327 94.0-96.8  10EtCO H H H B 341  11 n-PrCO H H H B 355  12 i-PrCO H H H B 355  13t-BuCO H H H B 369 108.0-114.0  14 PhCO H H H B 389 108.1-118.2  15PhCH₂CO H H H B 403  16 PhOCH₂CO H H H B 419  17 n-BuOCO H H H B 38586.5-94.0  18 H Val HCl H H D 384  19 H Phe HCl H H D 432  20 H Ala HClH H D 356  21 H PhCO H H D 389  22 H MeCO MeCO MeCO C 411  23 H EtCOEtCO EtCO C 453 75.9-79.9  24 H i-PrCO i-PrCO i-PrCO C 495  25 H PhCOPhCO PhCO C  26 H PhCO PhCO 3-Cl—PhCO C  27 n-BuOCO PhCO PhCO PhCO C 697 28 PhCH₂CO i-PrCO H H E 473  29 H n-PrCO C(CH₃)₃ D 395  30 H PhCOC(CH₃)₃ D 429  31 H Boc-Phe C(CH₃)₃ D 572  32 H i-PrCO C(CH₃)₃ D 395  33H H C(CH₃)₃ — 325 106.2-120.1  34 i-PrCO i-PrCO C(CH₃)₃ E 465  35 MeCOMeCO C(CH₃)₃ E 409 105.0-109.9  36 PhCO PhCO C(CH₃)₃ E 533  37 MeOCOMeOCO MeOCO MeOCO A 517  38¹ Val-NH-Boc H H H A 484 120.2-121.3  39 Hi-PrCO H H D 355  40² H i-PrCO H H D 355  41² H n-PrCO n-PrCO n-PrCO C495 52.6-58.4  42 C₈H₁₇OCO H H H B 441  43² H PhCO H H D 389   163-166.5 44 C₇H₁₅OCO H H H B 427  45² H i-BuCO i-BuCO i-BuCO C 537   142-142.8 46² H n-BuCO n-BuCO n-BuCO C 72.9-74.7  47 C₆H₁₃OCO H H H B 413134.4-136.0  48 H H i-PrCO i-PrCO F 425  49² H Ile HCl H H D 398  50² Ht-BuCO t-BuCO t-BuCO F 136.2-140    51 n-PrOCO H H H B 371  52n-C₅H₁₁OCO H H H B 399  53 i-BuOCO H H H B 385  54² H MeCO MeCO MeCO C411 88.0-90.9  55 i-PrCO i-PrCO i-PrCO i-PrCO A 565 60.4-64    56² Hi-PrCO i-PrCO i-PrCO A   145-146.9  57 MeOCO H H H B 141.1-141.8  58EtOCO H H H B 357  59² H EtCO EtCO EtCO C   72-75.2  60 PhCO EtCO EtCOEtCO C⁴ 557 54.6-56.9  61² H n-PrCO H H D 355  62² H PhCO PhCO PhCO D597 208.9-210.3  63² H n-C₅H₁₁CO H H D 383  64³ H COOC₆H₁₃ Hb H D 71.0-103.9  65³ H COOC₇H₁₅ H H D 90.9-94.6  66³ H COOC₈H₁₃ H H D70.5-81    67² H n-C₇H₁₅CO H H D 411  68² H Δ⁹-E H H D 549 n-C₁₈H₃₅CO 69 COO-i-Pr H H H D 371  70² H n-C₅H₁₁CO H H D 397  71² H n-C₁₁H₂₃CO HH D 154-155  72 H n-C₁₀H₂₁CO H H D   128-129.9  73² H n-C₉H₁₉CO H H D180.6-181.2  74 H n-C₁₃H₂₇CO H H D 495 116.8-128    75 H n-C₈H₁₉CO H H D  96-100.4  76 H n-C₆H₁₃CO H H D 55.3-56.5  77 H n-C₁₅H₃₁CO H H D 523  124-163.4  78 H Δ⁹-Z H H D   172-172.3 n-C₈H₁₇CO  79 COO-n-Bu CO-i-BuCO-i-Bu CO-i-Bu B/C⁶ 637  80 COO-n-Bu COEt COEt COEt B/C⁶ 553  81³ H HCO-n-C₅H₁₁ CO-n-C₅H₁₁ F 481  82³ H H CO-n-Bu CO-n-Bu F 453  83² H HCO-n-Bu COn-Bu F 124.3-128.4  84² H 4-methyl- H H D 187-189 benzoate 85² H CO-n-C₁₃H₂₇ H H D 178.6-179.4  86³ H COO-n- H H D   75-77.7C₁₀H₂₁  87 H CO-n-C₁₁H₂₃ H H D 467  88³ H H CO-n-Pr CO-n-Pr F   91-94.9 89² H H CO-n-Pr CO-n-Pr F 154.6-155.6  90² H COO-n-C₉H₁₉ H H D174.7-176.1  91² H H CO-i-Pr CO-i-Pr F 191.1-191.9  92² H H CO—Ph CO—PhF 166.2-168.1  93² H H CO—Et CO—Et F 194.6-198.2  94² H COO-n-PrCOO-n-Pr COO-n-Pr C 167.5-170.6  95⁵ H CO—Et CO—Et CO—Et C 149-153  96COO-n-C₅H₁₁ COO-n-C₅H₁₁ H H E   56-57.5  97 COO-n-C₆H₁₃ COO-n-C₆H₁₃ H HE  98² H CONH-n- H H D 164.9-168.5 C₈H₁₃  99 CO-n-C₅H₁₁ CO—Ph H H E 50367.4-73.9 100 CO-n-C₆H₁₃ CO—Ph H H E 517 70.2-74.6 101⁵ H H CO-n-BuCO-n-Bu F 115.3-120.1 105² H H CO-n-C₅H₁₁ CO-n-C₅H₁₁ F 127.3-128.6 103²H CO-n-Bu H H D 62.1-87.7

[0089] TABLE 1-A Cpd No. Chemical Name  1 Acetic acid(2R,3S,4R,5R)-3,4-diacetoxy-5-(4-acetylamino-2-oxo-2H-pyrimidin-1-yl)-2-azido-tetrahydro-furan-2-ylmethyl ester  2 Propionic acid(2R,3S,4R,5R)-2-azido-5-(2-oxo-4-propionylamino-2H-pyrimidin-1-yl)-3,4-bis-propionyloxy-tetrahydro-furan-2-ylmethyl ester  3 Butyric acid(2R,3S,4R,5R)-2-azido-5-(4-butyrylamino-2-oxo-2H-pyrimidin-1-yl)-3,4-bis-butyryloxy-tetrahydro-furan-2-ylmethyl ester  4 3-Methyl-butyric acid(2R,3S,4R,5R)-2-azido-5-[4-(3-methyl-butyrylamino)-2-oxo-2H-pyrimidin-1-yl]-4-(3-methyl-butyryloxy)-2-(3-methyl-butyryloxymethyl)-tetrahydro-furan-3-ylester  5 2,2-Dimethyl-propionic acid(2R,3S,4R,5R)-2-azido-5-[4-(2,2-dimethyl-propionylamino)-2-oxo-2H-pyrimidin-1-yl]-3,4-bis-(2,2-dimethyl-propionyloxy)-tetrahydro-furan-2-ylmethylester  6 Benzoic acid(2R,3S,4R,5R)-2-azido-3,4-dibenzoyloxy-5-(4-benzoylamino-2-oxo-2H-pyrimidin-1-yl)-tetrahydro-furan-2-ylmethyl ester  7 Phenoxy-acetic acid(2R,3S,4R,5R)-2-azido-5-[2-oxo-4-(2-phenoxy-acetylamino)-2H-pyrimidin-1-yl]-3,4-bis-(2-phenoxy-acetoxy)-tetrahydro-furan-2-ylmethyl ester  8[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid tert-butyl ester  9N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-acetamide  10N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-propionamide  11N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-rimidin-4-yl]-butyramide  12N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-isobutyramide  13N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-2,2-dimethyl-propionamide  14N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-benzamide  15N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-2-phenyl-acetamide  16N-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-2-phenoxy-acetamide  17[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid butyl ester  181-[(2R,3S,4R,5R)-5-(4-Amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethoxycarbonyl]-2-methyl-propyl-ammonium; chloride  191-[(2R,3S,4R,5R)-5-(4-Amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethoxycarbonyl]-2-phenyl-ethyl-ammonium; chloride  201-[(2R,3S,4R,5R)-5-(4-Amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethoxycarbonyl]-ethyl-ammonium; chloride  21 Benzoic acid(2R,3S,4R,5R)-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-y lmethyl ester  22 Acetic acid(2R,3S,4R,5R)-4-acetoxy-2-acetoxymethyl-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-tetrahydro-furan-3-yl ester  23 Propionic acid(2R,3S,4R,5R)-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-4-propionyloxy-2-propionyloxymethyl-tetrahydro-furan-3-yl ester  24 Isobutyric acid(2R,3S,4R,5R)-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-4-isobutyryloxy-2-isobutyryloxymethyl-tetrahydro-furan-3-yl ester  25 Benzoic acid(2R,3S,4R,5R)-3,4-dibenzoyloxy-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-tetrahydro-furan-2-ylmethyl ester  26 Benzoic acid(2R,3S,4R,5R)-3-(3-chloro-benzoyloxy)-4-benzoyloxy-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-tetrahydro-furan-2-ylmethyl ester  27 Benzoicacid(2R,3S,4R,5R)-3,4-dibenzoyloxy-2-azido-5-(4-butoxycarbonylamino-2-oxo-2H-pyrimidin-1-yl)-tetrahydro-furan-2-ylmethyl ester  28 Isobutyric acid(2R,3S,4R,5R)-2-azido-3,4-dihydroxy-5-[2-oxo-4-(2-phenoxy-acetylamino)-2H-pyrimidin-1-yl]-tetrahydro-furan-2-ylmethyl ester  29 Butyric acid(3aS,4R,6R,6aR)-6-(4-amino-2-oxo-2H-pyrimidin-1-yl)-4-azido-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethyl ester  30 Benzoic acid(3aS,4R,6R,6aR)-6-(4-amino-2-oxo-2H-pyrimidin-1-yl)4-azido-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethyl ester  312-tert-Butoxycarbonylamino-3-phenyl-propionic acid(3aS,4R,6R,6aR)-6-(4-amino-2-oxo-2H-pyrimidin-1-yl)-4-azido-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethylester  32 Isobutyric acid(3aS,4R,6R,6aR)-6-(4-amino-2-oxo-2H-pyrimidin-1-yl)-4-azido-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethyl ester  334-Amino-1-((3aR,4R,6R,6aS)-6-azido-6-hydroxymethyl-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-yl)-1 H-pyrimidin-2-one  34 Isobutyric acid(3aS,4R,6R,6aR)-4-azido-6-(4-isobutyrylamino-2-oxo-2H-pyrimidin-1-yl)-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethyl ester  35 Aceticacid(3aS,4R,6R,6aR)-6-(4-acetylamino-2-oxo-2H-pyrimidin-1-yl)-4-azido-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethyl ester  36 Benzoic acid(3aS,4R,6R,6aR)-4-azido-6-(4-benzoylamino-2-oxo-2H-pyrimidin-1-yl)-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethyl ester  37 Carbonicacid(2R,3R,4S,5R)-5-azido-2-(4-butoxycarbonylamino-2-oxo-2H-pyrimidin-1-yl)-4-butoxycarbonyloxy-5-butoxycarbonyloxy-methyl-tetrahydro-furan-3-yl esterbutyl ester  38¹1-[1-((2R,3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-ylcarbamoyl]-2-methyl-propyl-ammonium; chloride  39Isobutyric acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  40²(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-isobutyryloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  41²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-isobutyryloxy-5-isobutyryloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  42[(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid octyl ester  43²(S)-1-((3R,4S,5R)-5-Azido-5-benzoyloxymethyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  44[(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid heptyl ester  45²(S)-1-[(3R,4S,5R)-5-Azido-3,4-bis-(3-methyl-butyryloxy)-5-(3-methyl-butyryloxymethyl)-tetrahydro-furan-2-yl]-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride  46²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-pentanoyloxy-5-pentanoyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  47[(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid hexyl ester  48 Isobutyric acid(2R,3S,4R,5R)-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-2-hydroxymethyl-4-isobutyryloxy-tetrahydro-furan-3-yl ester  49²1-[(2R,3S,4R)-5-((S)-4-Amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethoxycarbonyl]-2-methyl-butyl-ammonium; chloride  50²(S)-1-[(2R,3S,4R)-5-azido-3,4-bis-(2,2-dimethyl-propionyloxy)-5-(2,2-dimethyl-propionyloxymethyl)-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride  51 Carbonic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester propyl ester  52 Carbonic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester pentyl ester  53 Carbonic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester isobutyl ester  54²(S)-1-((3R,4S,5R)-3,4-Diacetoxy-5-acetoxymethyl-5-azido-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  55 Isobutyric acid(2R,3S,4R)-2-azido-5-((S)-4-isobutyrylamino-2-oxo-2H-pyrimidin-1-yl)-4-isobutyryloxy-2-isobutyryloxymethyl-tetrahydro-furan-3-yl ester  56²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-isobutyryloxy-5-isobutyryloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  57[(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid methyl ester  58[(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid ethyl ester  59²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-propionyloxy-5-propionyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  60 Propionic acid(2R,3S,4R)-2-azido-5-((S)-4-benzoylamino-2-oxo-2H-pyrimidin-1-yl)-4-propionyloxy-2-propionyloxymethyl-tetrahydro-furan-3-yl ester  61²(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-propoxycarbonyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  62²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-benzoyloxy-5-benzoyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  63²(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-pentyloxycarbonyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  64³(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hexyloxycarbonyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; trifluoro-acetate  65³(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-heptyloxycarbonyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; trifluoro-acetate  66³(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-octyloxycarbonyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; trifluoro-acetate  67²(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-octanoyloxymethyl-tetrahydro-furan-2-yl)-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  68²(S)-1-[(3R,4S,5R)-5-Azido-3,4-dihydroxy-5-((E)-octadec-9-enoyloxymethyl)-tetrahydro-furan-2-yl]-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  69[(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamic acid isopropyl ester  70²(S)-1-((3R,4S,5R)-5-Azido-5-heptanoyloxymethyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  71²(S)-1-((3R,4S,5R)-5-Azido-5-dodecanoyloxymethyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  72 Undecanoic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  73²(S)-1-((3R,4S,5R)-5-Azido-5-decanoyloxymethyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  74 Tetradecanoic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  75 Nonanoic acid((2R,3S,4R)-5-((S)4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  76 Heptanoic acid((2R,3S,4R)-5-((S)4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  77 Hexadecanoic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  78 Z-Octadec-9-enoic acid(2R,3S,4R)-5-((S)4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  79 3-Methyl-butyric acid(2R,3S,4R)-2-azido-5-((S)-4-butoxycarbonylamino-2-oxo-2H-pyrimidin-1-yl)-3,4-bis-(3-methyl-butyryloxy)-tetrahydro-furan-2-ylmethyl ester  80Propionic acid(2R,3S,4R)-2-azido-5-((S)-4-butoxycarbonylamino-2-oxo-2H-pyrimidin-1-yl)-3,4-bis-propionyloxy-tetrahydro-furan-2-ylmethyl ester  81³(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-hexanoyloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; trifluoro-acetate  82³(S)-1-((3R,4S,5R)-5-azido-5-hydroxymethyl-3,4-bis-pentanoyloxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; trifluoro-acetate  83²(S)-1-((3R,4S,5R)-5-Azido-5-hydroxymethyl-3,4-bis-pentanoyloxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  84²(S)-1-[(3R,4S,5R)-5-Azido-3,4-dihydroxy-5-(4-methyl-benzoyloxymethyl)-tetrahydro-furan-2-yl]-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  85² (S)-1-((3R,4S,SR)-5-Azido-3,4-dihydroxy-5-tridecanoyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  86³(S)-1-((3R,4S,5R)-5-Azido-5-decyloxycarbonyloxymethyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; trifluoro-acetate  87Dodecanoic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester  88³(S)-1-((3R,4S,5R)-5-azido-3,4-bis-butyryloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; trifluoro-acetate  89²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-butyryloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  90²(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-nonyloxycarbonyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  91²(S)-1-((3R,4S,5R)-5-Azido-5-hydroxymethyl-3,4-bis-isobutyryloxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  92²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-benzoyloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  93²(S)-1-((3R,4S,5R)-5-Azido-5-hydroxymethyl-3,4-bis-propionyloxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  94²(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-butyryloxy-5-butyryloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  95²(S)-1-((3R,4S,5R)-5-azido-3,4-bis-propionyloxy-5-propionyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; methanesulfonate  96 Carbonicacid(2R,3S,4R)-2-azido-3,4-dihydroxy-5-((S)-2-oxo-4-pentyloxycarbonylamino-2H-pyrimidin-1-yl)-tetrahydro-furan-2-ylmethyl ester pentyl ester  97Carbonic acid(2R,3S,4R)-2-azido-5-((S)-4-hexyloxycarbonylamino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester hexyl ester  98²(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-octylcarbamoyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride  99 Benzoic acid(2R,3S,4R)-2-azido-5-((S)-4-hexanoylamino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester 100 Benzoic acid(2R,3S,4R)-2-azido-5-((S)-4-heptanoylamino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl ester 101⁵(S)-1-((3R,4S,5R)-5-azido-5-hydroxymethyl-3,4-bis-pentanoyloxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; methanesulfonate 102²(S)-1-((3R,4S,5R)-5-azido-3,4-bis-hexanoyloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; methanesulfonate 103²(S)-1-((3R,4S,5R)-5-Azido-3,4-dihydroxy-5-pentanoyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium; chloride

[0090] The compounds of formula I may be prepared by various methodsknown in the art of organic chemistry in general and nucleoside analoguesynthesis in particular. Specific methodologies to prepare compounds ofthe present invention are illustrated in Examples 1-6. The startingmaterials for the syntheses are either readily available from commercialsources or are known or may themselves be prepared by techniques knownin the art. General reviews of the preparation of nucleoside analoguesare included in the following publications which are incorporated hereinin their entirety:

[0091] A. M Michelson “The Chemistry of Nucleosides and Nucleotides”,Academic Press, New York 1963.

[0092] L. Goodman “Basic Principles in Nucleic Acid Chemistry” Ed P O PTs'O, Academic Press, New York 1974, Vol. 1, chapter 2.

[0093] “Synthetic Procedures in Nucleic acid Chemistry” Ed W W Zorbachand R S Tipson, Wiley, New York, 1973, Vol. 1 and 2.

[0094] H.Vorbrüggen and C. Ruh-Pohlenz (eds) “Handbook of NucleosideSynthesis” Wiley, New York, 2001.

[0095] The compounds of the present invention are prepared by acylationof a suitable nucleoside compound. Acylation of alcohols (J. March,Advanced Organic Chemistry John Wiley & Sons, New York 1992 392-398; J.Mulzer Synthesis of Esters, Activated Esters & Lactones in ComprehensiveOrganic Synthesis, E. Winterfeldt, ed., vol. 6, Pergamon Press, Oxford1991, pp.324-340) and amines (J. March, supra pp.417-425; H. G. Benz,Synthesis of Amides and Related Compounds in Comprehensive OrganicSynthesis, E. Winterfeldt, ed., vol. 6, Pergamon Press, Oxford 1991 pp.381-411) can be accomplished with a variety of acylating agentsincluding acid chlorides and acid anhydrides. These references areincorporated herein in their entirety. Other methods for activation of acarboxylic acid have been developed and can be utilized to prepare theprodrugs described herein. The extent and pattern of acylation iscontrolled by use of suitable protecting groups or by the delaying theintroduction of the basic amine into the pyrimidine base.

[0096] Tetraacyl nucleosides are readily prepared by acylating1-((2R,3R,4S,5R)-5-azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;hydrogen sulfate (II) with at least 4 equivalents of acylating agent(Method A; Example 1).

[0097] Amines typically are more reactive toward acylating agents thanare hydroxyl groups. Nonetheless to insure selective acylation of theamine substituent the hydroxyl groups are protected prior to acylation(Method B; Example 2). Trimethylsilyl ethers are useful protectinggroups for this transformation.

[0098] More detailed information regarding protection and deprotectionof alcohols and alternative protecting groups can be found in T. W.Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 3^(rd)edition, John Wiley & Sons, New York, 1999, and Harrison and Harrison etal., Compendium of Synthetic Organic Methods, Vols. 1-8 John Wiley andSons, 1971-1996. The above references are incorporated herein byreference in their entirety.

[0099] Selective acylation of the three hydroxy substuituents isaccomplished by carrying out the acylation on the corresponding uridinenucleoside II, which lacks the reactive amine substituent on theheteroaromatic ring, and subsequently converting the uridine to acytidine. The acylated uridine can be converted to cytidine by utilizingthe method described by A. D. Borthwick et al., (J. Med. Chem. 1990,33(1):179; see also K. J. Divakar and C. B. Reese J. Chem Soc., PerkinTrans. I 1982 1171-1176 and Maag et al. J. Med. Chem. 199235:1440-1451). The invention further provides a method for the selectivecleavage of the N-acyl moiety from a N acylated nucleoside by contactingthe N-acyl compound with zinc bromide in a protic solvent.

[0100] Selective acylation of the 5-hydroxy group and the amine wasaccomplished by protection of the vicinal 2′,3′-hydroxy groups of acarbohydrate before acylation of the primary alcohol (Method E; Example5). Protecting groups for vicinal diols often convert the diol into adioxolane or dioxane ring (see Greene supra; Harrison and Harrisonsupra). Most commonly these protecting groups include aldehydes andketones which readily form dioxolanes. Ketones which have foundparticular utility as diol protecting groups include acetone and C₅₋₇cycloalkanones. Cleavage of the dioxolane or dioxane to regenerate thediol is generally accomplished with aqueous acid and an organiccosolvent. Benzaldehyde readily forms acetals with vic diols which canbe deprotected by hydrogenolysis or acidic hydrolysis. Methoxysubstitution on the benzaldehyde increases the rate of acidic hydrolysisand also permits cleavage of the dioxolane under oxidative conditions,e.g. Ce(NH4)₂(NO₃)₆. Nitrobenzaldehydes afford dioxolanes which can bephotochemically cleaved. Cyclic orthoesters, e.g. ethoxymethylene acetalhave been utilized as diol protecting groups. These compounds can becleaved under mild acidic conditions; however the initial product is anester which must be hydrolyzed to regenerate the diol. The cyclic analog2-oxacyclopentylidene orthoester affords the diol directly upon acidhydrolysis. Cyclic carbonates and cyclic boronates also have found someutility as diol protecting groups. Any of these diol protecting groupscan be adapted to the present process. 5′-Monoacyl derivatives areaccessible by protection of the 2′,3′ vicinal diol of a uridinederivative. Acylation of the remaining reactive hydroxyl is followed byconversion of the uridine base to the corresponding cytidine base asdescribed above and deprotection of the vicinal diol (Method D; Example4). Alternatively the N-acyl group of an N,1′-diacyl cytidine compoundin which the 3′ and 4′ alcohols are protected can be selectively cleavedwith zinc bromide to produce the protected monoacyl compound which canbe further deprotected (R. Kierzek et al. Tetrahedron Lett. 1981 22(38):3762-64).

DOSAGE AND ADMINISTRATION

[0101] Compounds of the present invention may be administered eitheralone (i.e., monotherapy) or in combination with other therapeuticagents (e.g., “combination therapy”). Combination therapy can consist ofan HCV polymerase inhibitor and immune modulators which stimulatenatural immune responses to the virus and viral infected cells such asinterferons, chemically modified interferons, interleukin, tumornecrosis factor or colony stimulating factors. Compounds of the presentinvention also can be combined with other antiviral compounds with asimilar or complementary mode of action. Potential targets for antiviraldrugs have been reviewed. (see e.g.,E. DeClercq, Strategies in theDesign of Antiviral Drugs, Nature Rev Drug Discov. 2002 1(1):13-25; M.T. Reding, Recent Developments in hepatitis C antiviral research1999-2000, Exp Opin. Therap. Pat. 2000, 10(8):1201-1220) Antiviralcompounds including, but not limited to, HCV protease inhibitors, otherHCV polymerase inhibitors, HCV helicase inhibitors, HCV primaseinhibitors, HCV integrase inhibitors or HCV fusion inhibitors all couldby useful in combination with compounds of the present invention.

[0102] The compounds of the present invention may be formulated in awide variety of oral administration dosage forms and carriers. Whilenucleoside derivatives of the present invention are optimized fordelivery across the gastrointestinal mucosa, these compounds can beefficacious when administered by other routes of administration. Thepharmaceutically acceptable carriers may be either solid or liquid. Oraladministration can be in the form of tablets, coated tablets, dragées,hard and soft gelatine capsules, solutions, emulsions, syrups, orsuspensions. Compounds of the present invention are efficacious whenadministered by other routes of administration including continuous(intravenous drip) topical parenteral, intramuscular, intravenous,subcutaneous, transdermal (which may include a penetration enhancementagent), buccal, nasal, inhalation and suppository administration, amongother routes of administration. The preferred manner of administrationis generally oral using a convenient daily dosing regimen which can beadjusted according to the degree of affliction and the patient'sresponse to the active ingredient.

[0103] A compound or compounds of the present invention, as well astheir pharmaceutically useable salts, together with one or moreconventional excipients, carriers, or diluents, may be placed into theform of pharmaceutical compositions and unit dosages. The pharmaceuticalcompositions and unit dosage forms may be comprised of conventionalingredients in conventional proportions, with or without additionalactive compounds or principles, and the unit dosage forms may containany suitable effective amount of the active ingredient commensurate withthe intended daily dosage range to be employed. The pharmaceuticalcompositions may be employed as solids, such as tablets or filledcapsules, semisolids, powders, sustained release formulations, orliquids such as solutions, suspensions, emulsions, elixirs, or filledcapsules for oral use; or in the form of suppositories for rectal orvaginal administration; or in the form of sterile injectable solutionsfor parenteral use. A typical preparation will contain from about 5% toabout 95% active compound or compounds (w/w).

[0104] The term “excipient” as used herein refers to a compound that isuseful in preparing a pharmaceutical composition, generally safe,non-toxic and neither biologically nor otherwise undesirable, andincludes excipients that are acceptable for veterinary use as well ashuman pharmaceutical use. The term “excipient” as used herein includesboth one and more than one such excipient.

[0105] Solid form preparations include powders, tablets, pills,capsules, cachets, suppositories, and dispersible granules. A solidcarrier may be one or more substances which may also act as diluents,flavoring agents, solubilizers, lubricants, suspending agents, binders,preservatives, tablet disintegrating agents, or an encapsulatingmaterial. In powders, the carrier generally is a finely divided solidwhich is a mixture with the finely divided active component. In tablets,the active component generally is mixed with the carrier having thenecessary binding capacity in suitable proportions and compacted in theshape and size desired. Suitable carriers include but are not limited tomagnesium carbonate, magnesium stearate, talc, sugar, lactose, pectin,dextrin, starch, gelatin, tragacanth, methylcellulose, sodiumcarboxymethylcellulose, a low melting wax, cocoa butter, and the like.Solid form preparations include solutions, suspensions, and emulsions,and may contain, in addition to the active component, colorants,flavors, stabilizers, buffers, artificial and natural sweeteners,dispersants, thickeners, solubilizing agents, and the like.

[0106] The term “preparation” or “dosage form” as used herein isintended to include the formulation of the active compound withencapsulating material as carrier, providing a capsule in which theactive component, with or without carriers, is surrounded by a carrier,which is in association with it.

[0107] Similarly, cachets and lozenges are included. Tablets, powders,capsules, pills, cachets, and lozenges may be as solid forms suitablefor oral administration.

[0108] Liquid formulations also are suitable for oral administrationinclude liquid formulation including emulsions, syrups, elixirs, aqueoussolutions, aqueous suspensions are also suitable forms for oraladministration. These include solid form preparations which are intendedto be converted to liquid form preparations shortly before use.Emulsions may be prepared in solutions, for example, in aqueouspropylene glycol solutions or may contain emulsifying agents such aslecithin, sorbitan monooleate, or acacia. Aqueous solutions can beprepared by dissolving the active component in water and adding suitablecolorants, flavors, stabilizing, and thickening agents. Aqueoussuspensions can be prepared by dispersing the finely divided activecomponent in water with viscous material, such as natural or syntheticgums, resins, methylcellulose, sodium carboxymethylcellulose, and otherwell known suspending agents.

[0109] The compounds of the present invention may be formulated forparenteral administration (e.g., by injection, for example bolusinjection or continuous infusion) and may be presented in unit dose formin ampoules, pre-filled syringes, small volume infusion or in multi-dosecontainers with an added preservative. The compositions may take suchforms as suspensions, solutions, or emulsions in oily or aqueousvehicles, for example solutions in aqueous polyethylene glycol. Examplesof oily or nonaqueous carriers, diluents, solvents or vehicles includepropylene glycol, polyethylene glycol, vegetable oils (e.g., olive oil),and injectable organic esters (e.g., ethyl oleate), and may containformulatory agents such as preserving, wetting, emulsifying orsuspending, stabilizing and/or dispersing agents. Alternatively, theactive ingredient may be in powder form, obtained by aseptic isolationof sterile solid or by lyophilisation from solution for constitutionbefore use with a suitable vehicle, e.g., sterile, pyrogen-free water.

[0110] The compounds of the present invention may be formulated fortopical administration to the epidermis as ointments, creams or lotions,or as a transdermal patch. Ointments and creams may, for example, beformulated with an aqueous or oily base with the addition of suitablethickening and/or gelling agents. Lotions may be formulated with anaqueous or oily base and will in general also containing one or moreemulsifying agents, stabilizing agents, dispersing agents, suspendingagents, thickening agents, or coloring agents. Formulations suitable fortopical administration in the mouth include lozenges comprising activeagents in a flavored base, usually sucrose and acacia or tragacanth;pastilles comprising the active ingredient in an inert base such asgelatin and glycerin or sucrose and acacia; and mouthwashes comprisingthe active ingredient in a suitable liquid carrier.

[0111] The compounds of the present invention may be formulated foradministration as suppositories. A low melting wax, such as a mixture offatty acid glycerides or cocoa butter is first melted and the activecomponent is dispersed homogeneously, for example, by stirring. Themolten homogeneous mixture is then poured into convenient sized molds,allowed to cool, and to solidify.

[0112] The compounds of the present invention may be formulated forvaginal administration. Pessaries, tampons, creams, gels, pastes, foamsor sprays containing in addition to the active ingredient such carriersas are known in the art to be appropriate.

[0113] The compounds of the present invention may be formulated fornasal administration. The solutions or suspensions are applied directlyto the nasal cavity by conventional means, for example, with a dropper,pipette or spray. The formulations may be provided in a single ormultidose form. In the latter case of a dropper or pipette, this may beachieved by the patient administering an appropriate, predeterminedvolume of the solution or suspension. In the case of a spray, this maybe achieved for example by means of a metering atomizing spray pump.

[0114] The compounds of the present invention may be formulated foraerosol administration, particularly to the respiratory tract andincluding intranasal administration. The compound will generally have asmall particle size for example of the order of five (5) microns orless. Such a particle size may be obtained by means known in the art,for example by micronization. The active ingredient is provided in apressurized pack with a suitable propellant such as a chlorofluorocarbon(CFC), for example, dichlorodifluoromethane, trichlorofluoromethane, ordichlorotetrafluoroethane, or carbon dioxide or other suitable gas. Theaerosol may conveniently also contain a surfactant such as lecithin. Thedose of drug may be controlled by a metered valve. Alternatively theactive ingredients may be provided in a form of a dry powder, forexample a powder mix of the compound in a suitable powder base such aslactose, starch, starch derivatives such as hydroxypropylmethylcellulose and polyvinylpyrrolidine (PVP). The powder carrier will form agel in the nasal cavity. The powder composition may be presented in unitdose form for example in capsules or cartridges of e.g., gelatin orblister packs from which the powder may be administered by means of aninhaler.

[0115] When desired, formulations can be prepared with enteric coatingsadapted for sustained or controlled release administration of the activeingredient. For example, the compounds of the present invention can beformulated in transdermal or subcutaneous drug delivery devices. Thesedelivery systems are advantageous when sustained release of the compoundis necessary and when patient compliance with a treatment regimen iscrucial. Compounds in transdermal delivery systems are frequentlyattached to an skin-adhesive solid support. The compound of interest canalso be combined with a penetration enhancer, e.g., Azone(1-dodecylaza-cycloheptan-2-one). Sustained release delivery systems areinserted subcutaneously into to the subdermal layer by surgery orinjection. The subdermal implants encapsulate the compound in a lipidsoluble membrane, e.g., silicone rubber, or a biodegradable polymer,e.g., polyactic acid.

[0116] Suitable formulations along with pharmaceutical carriers,diluents and expcipients are described in Remington: The Science andPractice of Pharmacy 1995, edited by E. W. Martin, Mack PublishingCompany, 19th edition, Easton, Pennsylvania. A skilled formulationscientist may modify the formulations within the teachings of thespecification to provide numerous formulations for a particular route ofadministration without rendering the compositions of the presentinvention unstable or compromising their therapeutic activity.

[0117] The modification of the present compounds to render them moresoluble in water or other vehicle, for example, may be easilyaccomplished by minor modifications (salt formulation, esterification,etc.), which are well within the ordinary skill in the art. It is alsowell within the ordinary skill of the art to modify the route ofadministration and dosage regimen of a particular compound in order tomanage the pharmacokinetics of the present compounds for maximumbeneficial effect in patients.

[0118] The phrase “therapeutically effective amount” as used hereinmeans an amount required to reduce symptoms of the disease in anindividual. The dose will be adjusted to the individual requirements ineach particular case. That dosage can vary within wide limits dependingupon numerous factors such as the severity of the disease to be treated,the age and general health condition of the patient, other medicamentswith which the patient is being treated, the route and form ofadministration and the preferences and experience of the medicalpractitioner involved. For oral administration, a daily dosage ofbetween about 0.01 and about 100 mg/kg body weight per day should beappropriate in monotherapy and/or in combination therapy. A preferreddaily dosage is between about 0.1 and about 500 mg/kg body weight, morepreferred 0.1 and about 100 mg/kg body weight and most preferred 1.0 andabout 10 mg/kg body weight per day. Thus, for administration to a 70 kgperson, the dosage range would be about 0.7 g to 7.0 g per day. Thedaily dosage can be administered as a single dosage or in divideddosages, typically between 1 and 5 dosages per day. Generally, treatmentis initiated with smaller dosages which are less than the optimum doseof the compound. Thereafter, the dosage is increased by small incrementsuntil the optimum effect for the individual patient is reached. One ofordinary skill in treating diseases described herein will be able,without undue experimentation and in reliance on personal knowledge,experience and the disclosures of this application, to ascertain atherapeutically effective amount of the compounds of the presentinvention for a given disease and patient.

[0119] The pharmaceutical preparations are preferably in unit dosageforms. In such form, the preparation is subdivided into unit dosescontaining appropriate quantities of the active component. The unitdosage form can be a packaged preparation, the package containingdiscrete quantities of preparation, such as packeted tablets, capsules,and powders in vials or ampoules. Also, the unit dosage form can be acapsule, tablet, cachet, or lozenge itself, or it can be the appropriatenumber of any of these in packaged form.

[0120] The pharmaceutical compositions in Example 8 are given to enablethose skilled in the art to more clearly understand and to practice thepresent invention. They should not be considered as limiting the scopeof the invention, but merely as being illustrative and representativethereof.

[0121] The following preparations and examples are given to enable thoseskilled in the art to more clearly understand and to practice thepresent invention. They should not be considered as limiting the scopeof the invention, but merely as being illustrative and representativethereof.

[0122] Efforts have been made to ensure accuracy with respect to numbersused (e.g., amounts, temperatures), but allowance for some experimentalerror and deviation, including differences in calibration, rounding ofnumbers, and the like, is contemplated.

EXAMPLE 1 Method A: Preparation of N, 2′, 3′, 4′-Tetraacyl NucleosideDerivatives

[0123] Acetic acid3,4-diacetoxy-5-(4-acetylamino-2-oxo-2H-pyrimidin-1-yl)-2-azido-tetrahydro-furan-2-ylmethylester

[0124] A stirred suspension of 4′-azidocytidine hemisulfate (0.30 g),dimethylaminopyridine (cat.), and N,N-diisopropylethylamine (3.69 mL) inmethylene chloride (5 mL), under inert atmosphere, was cooled in anice/water bath and treated dropwise with acetyl chloride (0.452 mL) andacetic anhydride (0.60 mL). The mixture was allowed to warm to ambienttemperature and after 2 days was subjected, untreated, to flashchromatography (50% ethyl acetate in hexanes, then 75% ethyl acetate inhexanes, then 100% ethyl acetate, then 5% methanol in ethyl acetate) toafford 0.335 g of the solid product (compound 1; M+H=453

EXAMPLE 2 Method B: Preparation of N-acyl Nucleoside Derivatives

[0125][1-(5-Azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl]-carbamicacid butyl ester

[0126] A stirred suspension of 4′-azidocytidine hemisulfate (0.50 g) inpyridine (8 mL), under inert atmosphere, was cooled in an ice/water bathand treated with trimethylsilyl chloride (1 mL). The mixture was allowedto warm to ambient temperature and after 1 h was treated with butylchloroformate (0.2 mL). After stirring another 2 h at that temperature,the reaction was cooled in an ice/water bath and treated with 5 mLaqueous ammonium bicarbonate. The organics were extracted twice withmethylene chloride, dried over magnesium sulfate, and filtered. To thefiltrate was added tetra-n-butyl ammonium fluoride (0.25 mL, 1 M intetrahydrofuran). The reaction was stirred at ambient temperature forthree days. After solvent removal, the residue was subjected to flashchromatography (25% hexanes in ethyl acetate, then ethyl acetate, then6.5% methanol in ethyl acetate) to afford 400 mg of the product as asolid (compound 17; mp 86.5-94° C.).

EXAMPLE 3 Method C: Preparation of 2′, 3′, 5′-Triacyl NucleosideDerivatives

[0127] Acetic acid3,4-diacetoxy-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-tetrahydro-furan-2-ylmethylester (22)

[0128] Step 1

[0129] To a stirred solution containing 0.330 g (1.15 mmol)4′-azidouridine, 2 mL pyridine and 2 mL acetic anhydride was added 0.010g (0.08 mmol) of 4-dimethylaminopyridine. After 12 h, the reactionmixture was evaporated to dryness under reduced pressure. The residuewas dissolved in dichloromethane and washed with saturated aqueoussodium hydrogen carbonate solution, dried over magnesium sulfate andevaporated to dryness to give 0.42 g (88%) of2′,3′,5′-tri-acetoxy-4′-azidouridine (IIIa: R═CH₃).

[0130] Step 2

[0131] POCl₃ (0.31 mL; 3.304 mmol) was added to a stirred mixturecontaining 0.340 g (0.826 mmol) of the uridine, 0.913 g (13.22 mmol) of1,2,4-triazole and 2.30 mL (16.52 mmol) of triethylamine in 20 mLacetonitrile cooled to 5° C. The reaction mixture was allowed to warm toroom temperature. After 12 h, the reaction mixture was evaporated todryness under reduced pressure. The residue was diluted withdichloromethane, washed with saturated aqueous sodium hydrogen carbonatesolution, dried over magnesium sulfate and evaporated to dryness to give0.300 g (78%) of (IIc: R═CH₃).

[0132] Step 3

[0133] To a sealed flask containing 0.066 g (1.254 mmol) ammoniumchloride and 0.070 g (1.254 mmol) of potassium hydroxide was added 10 mLacetonitrile, 20 mL water, 0.190 mL (1.278 mmol) of triethylaminefollowed by a solution containing 0.290 g (0.627 mmol) of the triazolein 10 mL acetonitrile. After 12 h, the mixture was evaporated to drynessunder reduced pressure. The residue was dissolved in ethyl acetate andwashed with water, dried over magnesium sulfate and evaporated todryness under reduced pressure. Chromatography (10% methanol indichloromethane) provided 0.060 g (23%) of the cytidine. (IId; R═CH₃;compound 22; MH⁺=411; MNa⁺=433).

[0134] Proceeding in similar fashion with the appropriate acylatingagent there was obtained isobutyric acid5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-3,4-bis-isobutyryloxy-tetrahydro-furan-2-ylmethylester (compound 24; MH⁺=495; MNa⁺=517) and benzoic acid5-(4-amino-2-oxo-2H-pyrimidin-1-yl)3,4-di-benzoxy-tetrahydro-furan-2-ylmethylester (compound 25).

EXAMPLE 4 Method D: Preparation of 5′-Acyl Nucleoside Derivatives

[0135] 2-Amino-3-phenyl-propionic acid5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethylester hydrochloride (Ie: R═CH(NH₃ ⁺)CHC₂C₆H₅Cl; compound 19)

[0136] Step 1

[0137]1-(6-Hydroxymethyl-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-yl)-1H-pyrimidine-2,4-dione(IIIb; compound 33)

[0138] A mixture containing 3.0 g (10.5 mmol) of 4′-azidouridine, 0.05 g(0.26 mmol) p-toluenesulfonic acid monohydrate and 6 mL (48.8 mmol)2,2-dimethoxypropane in 20 mL acetone was stirred at room temperaturefor 12 h. The reaction mixture was diluted with ethyl acetate, washedwith saturated aqueous sodium hydrogen carbonate solution, dried overmagnesium sulfate and evaporated to dryness under reduced pressure togive the desired product 2.20 g (64%) of as a white solid.

[0139] Step 2

[0140] 2-tert-Butoxycarbonylamino-3-phenyl-propionic acid6-(2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethylester (IIIb: R═COCH(NH-boc)CH₂C₆H₅)

[0141] To a stirred solution containing 1.00 g (3.07 mmol) of 4′azido-2′,3′-O-iso-propyl-uridine, 1.63 g (6.14 mmol) Boc-L-phenylalanineand 1.18 g (6.14 mmol) 1-(3-dimethylaminopropyl)-3-ethylcarbodimidehydrochloride in 20 mL N,N-dimethylformamide was added 0.375 g (3.07mmol) of 4-dimethylaminopyridine. The resulting solution was left tostir under an atmosphere of nitrogen and at room temperature. After 12h, the reaction mixture was evaporated to dryness under reducedpressure. Chromatography (0 to 100% ethyl acetate in hexanes) of thecrude residue gave 1.01 g (57%) of the desired product as a white foam(MH⁺=573; MNa⁺=595).

[0142] Step 3

[0143] 2-tert-Butoxycarbonylamino-3-phenyl-propionic acid6-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-ylmethylester (IIe: R═CH(NHboc)CH₂C₆H₅₎

[0144] POCl₃ (0.651 mL; 6.98 mmol) was added to a stirred mixturecontaining 1.00 g (1.746 mmol) of the uridine, 1.93 g (27.94 mmol) of1,2,4-triazole and 4.86 mL (34.93 mmol) of triethylamine in 50 mLacetonitrile cooled to 5° C. The reaction mixture was allowed to warm toroom temperature. After 12 h, the reaction mixture was evaporated todryness under reduced pressure. The residue was diluted withdichloromethane, washed with saturated aqueous sodium hydrogen carbonatesolution, dried over magnesium sulfate and evaporated to dryness to give1.0 g (92%) of the triazole.

[0145] To a sealed flask containing 0.171 g (3.207 mmol) ammoniumchloride and 0.180 g (3.207 mmol) of potassium hydroxide was added 10 mLacetonitrile, 20 mL water, 0.446 mL (3.207 mmol) of triethylaminefollowed by a solution containing 1.00 g (1.603 mmol) of thephenylalanineuridine in 10 mL acetonitrile. After 12 h, the mixture wasevaporated to dryness under reduced pressure. The residue was dissolvedin ethyl acetate and washed with water, dried over magnesium sulfate andevaporated to dryness under reduced pressure. Chromatography (10%methanol in dichloromethane) provided 0.48 g (52%) of the cytidine.(MH⁺=572; MNa⁺=594).

[0146] Step 4:

[0147] 2-Amino-3-phenyl-propionic acid5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethylester hydrochloride (Ie: R═CH(NH⁺)CH₂C₆H₅Cl⁻)

[0148] To a solution containing 0.23 g (0.402 mmol) of phenylalaninecytidine (IIe: R═CH(NHBoc)CH₂Ph) in 10 mL of methanol was added 0.079 mL(0.804 mmol) concentrated hydrogen chloride solution. After 12 h, thereaction mixture was evaporated to dryness. The residue was dissolved inwater and washed with ethyl acetate and evaporated to dryness underreduced pressure to give 0.160 g (94%) cytidine product (compound 19).

[0149] In similar fashion substituting boc-L-valine and boc-L-alaninethere was obtained respectively, 2-amino-3-methyl-butyric acid5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethylester hydrochloride (compound 18; MH⁺=384; MNa⁺=406) and2-amino-propionic acid5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethylester hydrochloride (compound 20; MH⁺=356; MNa⁺=378).

[0150] In similar manner utilizing benzoic anhydride there was obtainedbenzoic acid5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethylester (compound 14; MH⁺=389; MNa⁺=411).

EXAMPLE 5 Method E

[0151] Isobutyric acid2-azido-3,4-dihydroxy-5-(2-oxo-4-phenylacetylamino-2H-pyrimidin-1-yl)-tetrahydro-furan-2-ylmethylester

[0152] Step 1

[0153] A solution of4-amino-1-(6-azido-6-hydroxymethyl-2,2-dimethyl-tetrahydro-furo[3,4-d][1,3]dioxol-4-yl)-1H-pyrimidin-2-one(II, 0.14 g), 4-nitrophenyl phenylacetate (0.12 g) and1-hydroxybenzotriazole (0.06 g) in DMF (15 mL) was stirred at roomtemperature overnight. Water (15 mL) was added and the mixture was twiceextracted with ethyl acetate. The combined ethyl acetate extracts werewashed with water and brine and dried over anhydrous magnesium sulfate.The solution was concentrated in vacuo and purified by flash columnchromatography which yielded IIh (0.18 g) as a colorless oil.

[0154] Step 2

[0155] IIh from the previous step (0.18 g), triethylamine (0.07 ml) anddimethylaminopyridine (0.01 g) were dissolved in THF (15 ml) and stirredat room temperature under nitrogen atmosphere. Isobutyroyl chloride(0.043 mL) was added slowly and the reaction was stirred at rt for 6hours. Water (15 mL) was added and the mixture was extracted twice withethyl acetate. The combined extracts were dried over anhydrous magnesiumsulfate, filtered, and the solution concentrated in vacuo. The product(IIi; 0.18 g) was separated by a flash column chromatography as an oil.

[0156] Step 3

[0157] IIi (0.18 g) was dissolved in acetic acid (60%) and stirred at100° C. overnight. The reaction was cooled to rt and the solventevaporated under reduced pressure. The product was purified bypreparatory thin layer chromatography. The crude product (69 mg) wasdissolved in THF (10 ml) and treated at room temperature with4-nitrophenyl phenylacetate (55 mg) and 1-hydroxybenzotriazole (26 mg).The reaction mixture was stirred at rt overnight. The solvent wasevaporated and the residue was re-purified by preparatory thin layerchromatography to afford IIj (17 mg) as a colorless oil.

EXAMPLE 6

[0158] Method F

[0159] Isobulyric acid(2R,3S,4R,5R)-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-2-hydroxymethyl-4-isobutyryloxy-tetrahydro-furan-3-ylester

[0160] Step 1

[0161] A flask was charged with 1 (0.610 g; 1.75 mmol),dimethyl-tert-butylsilane (0.580 g; 3.84 mmol), imidazole (0.262 g;3.842 mmol) and DMF (12 mL) and the resulting homogenous solution wasstirred overnight at rt. Mass spectroscopy indicated the crude productwas a mixture of mono- and disilylated product. The solvent was removedin vacuo and the residue was dissolved in pyridine (12 mL) and CH₂Cl₂(12 mL) and a small catalytic quantity of DMAP and isobutyric anhydride(0.96 mL; 5.76 mmol) was added and the resulting mixture was stirredovernight at rt. The reaction mixture was extracted with a mixture ofwater and saturated NaHCO₃ and the aqueous layer back-extracted CH₂Cl₂.The organic layers were combined and extracted with IN HCl and water,dried (MgSO₄), filtered and evaporated to yield 1.3 g of crude silylatednucleosides as a yellow oil.

[0162] Step 2

[0163] The crude product (1.3 g) from the previous step was dissolved inTHF (20 mL) and tetrabutyl ammonium fluoride (0.5 mL; TBAF; 1.0Msolution in THF) was added and the reaction mixture was allowed to stirovernight. After 16 h, another 0.5 mL aliquot of TBAF was added andstirring continued for another 4 h and the solvent was evaporated. Theresidue was partitioned between CH₂Cl₂ and a mixture of H₂O andsaturated NaHCO₃. The aqueous extract was washed with CH₂Cl₂ and thecombined organic extracts were washed with H₂O and aqueous NaCl, dried,filtered and evaporated. The crude product was purified by flashchromatography and eluted with a gradient (CH₂Cl₂→4% MeOH/CH₂Cl₂) toyield a colorless white solid N, 2′,3′-tri-isobutyrate (IIk; 140 mg)

[0164] Step 3

[0165] The tri-isobutyrate (140 mg; 0.283 mmol) was dissolve in 2.5 mLCH₂Cl₂ and 0.8 mL of MeOH. To the resulting solution was added ZnBr₂ (6mg; 0.283 mmol) and the resulting solution was stirred at 65° C.overnight. The solvent was removed in vacuo to yield 150 mg of a yellowfoam which was purified by flash chromatography on silica gel and elutedwith a gradient (CH₂Cl₂→75% MeOH/CH₂Cl₂) to yield IIm (R=i-Pr) as awhite solid (0.120 g; 98% theory).

EXAMPLE 7 Plasma Pharmacokinectics

[0166] Pharmacokinetic procedures were used to determine plasma levelsof4-amino-1-((2R,3R,4S,5R)-5-azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-1H-pyrimidin-2-one(II) after administration of a single oral 5 mg/kg dose of a prodrug ofII. The formulation is a solution/suspension containing 0.0176 mmol ofprodrug in 5 mL of an appropriate vehicle.

[0167] Three unfasted male Cynomolgus monkeys (6-9 kg) were fitted witha saphenous or brachial catheter to facilitate blood draw. Free accessto food and water will be allowed at all times during the study. On theday of the study a predose blood sample (2-3 mL) was taken from eachmonkey. The monkeys were dosed with 1 mL/kg of the dose solution by oralgavage. At each of the following time points (0.25, 0.5, 1, 3, 5, 7, 10,24, 32, and 48 hour) after dosing, approximately 0.5 mL of blood will becollected into lithium heparin-coated tubes. Blood was centrifuged toobtain plasma which was frozen until analysis.

[0168] The concentration of Ia (R¹—R⁴═H) in each plasma sample wasdetermined by an LC-MS assay. Standard curves were prepared in blankmonkey plasma. The AUC represents the area under a plot of concentrationvs time total which describes the concentration of the drug in systemiccirculation as a function of time(L. Z. Benet, D. L. Kroetz and L. B.Sheiner Pharmacokinetics in Goodman & Gilman's The Pharmacological Basisof Therapeutics, J. G. Hardman & L. E. Limbird Eds., 9^(th) Edition,McGraw Hill, New York, p 17-23). Cmax is the peak concentration which isfound. AUC Cmax Cpd AUC_(0-24 h) fold Cmax fold No. (μg · h/mL) increase(μg/mL) increase II 2.85 1.00 0.312 1.00 24 10.5 3.83 1.42 4.55 46 12.014.23 2.21 6.33 82 12.96 4.56 1.73 4.96 86 10.41 9.67 1.69 4.84

EXAMPLE 7 Renilla Luciferase Assay

[0169] This assay measures the ability of the compounds of formula I toinhibit HCV RNA replication, and therefore their potential utility forthe treatment of HCV infections. The assay utilizes a reporter as asimple readout for intracellular HCV replicon RNA level. The Renilla.luciferase gene was introduced into the first open reading frame of areplicon construct NK5.1 (Krieger et al., J. Virol. 75:4614),immediately after the internal ribosome entry site (IRES) sequence, andfused with the neomycin phosphotransferase (NPTII) gene via aself-cleavage peptide 2A from foot and mouth disease virus (Ryan & Drew,EMBO Vol 13:928-933). After in vitro transcription the RNA waselectroporated into human hepatoma Huh7 cells, and G418-resistantcolonies were isolated and expanded. Stably selected cell line 2209-23contain replicative HCV subgenomic RNA, and the activity of Renillaluciferase expressed by the replicon reflects its RNA level in thecells. The assay was carried out in duplicate plates, one in opaquewhite and one in transparent, in order to measure the anti-viralactivity and cytotoxicity of a chemical compound in parallel ensuringthe observed activity is not due to decreased cell proliferation.

[0170] Renilla luciferase HCV replicon cells (2209-23) cultured inDulbecco's MEM (GibcoBRL cat no. 31966-021) with 5% fetal calf serum(FCS, GibcoBRL cat. no. 10106-169) were plated onto a 96-well plate at5000 cells per well, and incubated overnight. Twenty-four hours later,different dilutions of chemical compounds in the growth medium wereadded to the cells, which were then further incubated at 37° C. forthree days. At the end of the incubation time, the cells in white plateswere harvested and luciferase activity was measured by usingDual-Luciferase reporter assay system (Promega cat no. El 960) All thereagents described in the following paragraph were included in themanufacturers kit, and the manufacturer's instructions were followed forpreparations of the reagents. The cells were washed twice with 200 μl ofphosphate buffered saline (pH 7.0) (PBS) per well and lysed with 25 μlof 1× passive lysis buffer prior to incubation at room temperature for20 min. One hundred microlitre of LAR II reagent was added to each well.The plate was then inserted into the LB 96V microplate luminometer(MicroLumatPlus, Berthold), and 100 μl of Stop & Glo® reagent wasinjected into each well and the signal measured using a 2-second delay,10-second measurement program. IC₅₀, the concentration of the drugrequired for reducing replicon level by 50% in relation to the untreatedcell control value, can be calculated from the plot of percentagereduction of the luciferase activity vs. drug concentration.

[0171] WST-1 reagent from Roche Diagnostic (cat no. 1644807) was usedfor the cytotoxicity assay. Ten microlitre of WST-1 reagent was added toeach well including wells that contain media alone as blanks. Cells werethen incubated for 1 to 1.5 hours at 37° C., and the OD value wasmeasured by a 96-well plate reader at 450 nm (reference filter at 650nm). Again CC₅₀, the concentration of the drug required for reducingcell proliferation by 50% in relation to the untreated cell controlvalue, can be calculated from the plot of percentage reduction of theWST-1 value vs. drug concentration. Luciferase Compound Activity NumberIC₅₀ (μM) 5 5.33 18 2.4 25 2.47

EXAMPLE 8

[0172] Pharmaceutical compositions of the subject Compounds foradministration via several routes were prepared as described in thisExample.

Composition for Oral Administration (A)

[0173] Ingredient % wt./wt. Active ingredient 20.0% Lactose 79.5%Magnesium stearate  0.5%

[0174] The ingredients are mixed and dispensed into capsules containingabout 100 mg each; one capsule would approximate a total daily dosage.

Composition for Oral Administration (B)

[0175] Ingredient % wt./wt. Active ingredient 20.0% Magnesium stearate 0.5% Crosscarmellose sodium  2.0% Lactose 76.5% PVP(polyvinylpyrrolidine)  1.0%

[0176] The ingredients are combined and granulated using a solvent suchas methanol. The formulation is then dried and formed into tablets(containing about 20 mg of active compound) with an appropriate tabletmachine.

Composition for Oral Administration (C)

[0177] Ingredient % wt./wt. Active compound 1.0 g Fumaric acid 0.5 gSodium chloride 2.0 g Methyl paraben 0.15 g Propyl paraben 0.05 gGranulated sugar 25.5 g Sorbitol (70% solution) 12.85 g Veegum K(Vanderbilt Co.) 1.0 g Flavoring 0.035 ml Colorings 0.5 mg Distilledwater q.s. to 100 ml

[0178] The ingredients are mixed to form a suspension for oraladministration.

Parenteral Formulation (D)

[0179] Ingredient % wt./wt. Active ingredient 0.25 g Sodium Chloride qsto make isotonic Water for injection to  100 ml

[0180] The active ingredient is dissolved in a portion of the water forinjection. A sufficient quantity of sodium chloride is then added withstirring to make the solution isotonic. The solution is made up toweight with the remainder of the water for injection, filtered through a0.2 micron membrane filter and packaged under sterile conditions.

Suppository Formulation (E)

[0181] Ingredient % wt./wt. Active ingredient  1.0% Polyethylene glycol1000 74.5% Polyethylene glycol 4000 24.5%

[0182] The ingredients are melted together and mixed on a steam bath,and poured into molds containing 2.5 g total weight.

Topical Formulation (F)

[0183] Ingredients grams Active compound 0.2-2 Span 60 2 Tween 60 2Mineral oil 5 Petrolatum 10 Methyl paraben 0.15 Propyl paraben 0.05 BHA(butylated hydroxy anisole) 0.01 Water q.s. 100

[0184] All of the ingredients, except water, are combined and heated toabout 60° C. with stirring. A sufficient quantity of water at about 60°C. is then added with vigorous stirring to emulsify the ingredients, andwater then added q.s. about 100 g.

Nasal Spray Formulations (G)

[0185] Several aqueous suspensions containing from about 0.025-0.5percent active compound are prepared as nasal spray formulations. Theformulations optionally contain inactive ingredients such as, forexample, microcrystalline cellulose, sodium carboxymethylcellulose,dextrose, and the like. Hydrochloric acid may be added to adjust pH. Thenasal spray formulations may be delivered via a nasal spray metered pumptypically delivering about 50-100 microliters of formulation peractuation. A typical dosing schedule is 2-4 sprays every 4-12 hours.

[0186] The features disclosed in the foregoing description, or thefollowing claims, or the accompanying drawings, expressed in theirspecific forms or in terms of a means for performing the disclosedfunction, or a method or process for attaining the disclosed result, asappropriate, may, separately, or in any combination of such features, beutilized for realizing the invention in diverse forms thereof.

[0187] The foregoing invention has been described in some detail by wayof illustration and example, with reference to the specific embodimentsfor purposes of clarity and understanding. It will be obvious to one ofskill in the art that changes and modifications may be made andequivalents substituted without departing from the true spirit and scopeof the invention. Therefore, it is to be understood that the abovedescription is intended to be illustrative and not restrictive. Manymodifications may be made to adapt a particular situation, material,composition of matter, process, or process step or steps, to theobjective spirit and scope of the present invention. All suchmodifications are intended to be within the scope of the claims appendedhereto

[0188] All patents, patent applications and publications cited in thisapplication are hereby incorporated by reference in their entirety forall purposes to the same extent as if each individual patent, patentapplication or publication were so individually denoted.

We claim:
 1. A compound of formula I

wherein: R¹ and R² are independently selected from the group consistingof hydrogen, COR⁵, C(═O)OR⁵, C(═O)SR⁵, C(═O)NHR⁵ and COCH(R⁶)NHR⁷; R³and R⁴ are independently selected from the group consisting of hydrogenCOR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; or, R³ and R⁴ taken togetherare selected from the group consisting of CH₂, C(CH₃)₂ and CHPh; R⁵isindependently selected from the group consisting of C₁₋₁₈ unbranched orbranched alkyl, C₁₋₁₈ unbranched or branched alkenyl, C₁₋₁₈ unbranchedor branched alkynyl, C₁₋₁₈ lower haloalkyl, C₃₋₈ cycloalkyl, alkylsubstituted C₃₋₈ cycloalkyl, phenyl optionally substituted with one tothree substituents independently selected from the group consisting ofhalo, lower alkyl, lower alkoxy, lower thioalkyl, lower alkyl sulfinyl,lower alkyl sulfonyl, nitro, cyano, CH₂Ph wherein in phenyl ring isoptionally substituted as described above, and CH₂OPh wherein in phenylring is optionally substituted as described above; R⁶ is independentlyselected from the group consisting of the side chains of naturallyoccurring amino acids and C₁₋₅ unbranched or branched alkyl; R⁷ isselected from the group consisting of hydrogen, R⁵OCO; or, R⁶ andR⁷taken together are (CH₂)₃; and, hydrates, solvates, clathrates andacid addition salts thereof; with the proviso that at least one of R¹,R², R³, or R⁴ is other than hydrogen.
 2. A compound according to claim 1wherein R¹, R², R³, and R⁴ each are independently COR⁵, C(═O)OR⁵,C(═O)SR⁵ and each R⁵ is independently selected from the group consistingof C₁₋₁₈ unbranched or branched lower alkyl, phenyl and CH₂OPh.
 3. Acompound according to claim 2 wherein R¹, R², R³, and R⁴ are COR⁵ andeach R⁵ is independently selected from the group consisting of C₁₋₁₈unbranched or branched lower alkyl, phenyl and CH₂OPh.
 4. A compoundaccording to claim 1 wherein R¹ is COR⁵, C(═O)OR⁵, C(═O)SR⁵ orCOCH(R⁶)NHR⁷ and R², R³ and R⁴ are hydrogen.
 5. A compound according toclaim 4 wherein R⁵ is selected from a group consisting of C₁₋₁₈unbranched or branched lower alkyl, C₃₋₈ cycloalkyl, phenyl and CH₂OPh,or R⁶ is selected from the group consisting of C₁₋₅ unbranched orbranched alkyl and the side chain of a naturally occurring amino acid.6. A compound according to claim 1 wherein R² is selected from the groupconsisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵, and COCH(R⁶)NHR⁷, R¹, R³ and R⁴are hydrogen.
 7. A compound according to claim 6 wherein R⁵ is selectedfrom the group consisting of is C₁₋₁₈ unbranched or branched alkyl, C₃₋₈cycloalkyl and phenyl or R⁶ is C₁₋₅ unbranched or branched alkyl or theside chain of a naturally occurring amino acid.
 8. A compound accordingto claim 6 wherein R² is COCH(R⁶)NH₂ and R⁶ is selected from the groupconsisting of C₁₋₅ unbranched or branched alkyl and CH₂Ph.
 9. A compoundaccording to claim 1 wherein R³ and R⁴ both are hydrogen.
 10. A compoundaccording to claim 1 wherein R¹ is hydrogen and R², R³ and R⁴ areindependently selected from the group consisting of COR⁵, C(═O)OR⁵andC(═O)SR⁵.
 11. A compound according to claim 1 wherein R¹ is hydrogen, R²is selected from the group consisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ andCOCH(R⁶)NHR⁷, and R³ and R⁴ taken together are selected from the groupconsisting of CH₂, C(CH₃)₂ and CHPh.
 12. A compound according to claim 1wherein R¹ and R² are hydrogen and R³ and R⁴ are independently selectedfrom the group consisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷wherein R⁷ is hydrogen.
 13. A compound according to claim 1 wherein R¹and R² are independently selected from the group consisting of COR⁵,C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷, and R³ and R⁴ taken together areselected from the group consisting of CH₂, C(CH₃)₂ and CHPh.
 14. Acompound according to claim 1 selected from the group consisting of:Isobutyric acid(2R,3S,4R,5R)-5-(4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-4-isobutyryloxy-2-isobutyryloxymethyl-tetrahydro-furan-3-ylester;(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-propionyloxy-5-propionyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride;(S)-1-((3R,4S,5R)-5-Azido-3,4-bis-pentanoyloxy-5-pentanoyloxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride;(S)-1-[(3R,4S,5R)-5-Azido-3,4-dihydroxy-5-(4-methyl-benzoyloxymethyl)-tetrahydro-furan-2-yl]-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;chloride;(S)-1-((3R,4S,5R)-5-azido-3,4-bis-hexanoyloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;methanesulfonate;(S)-1-((3R,4S,5R)-5-azido-5-hydroxymethyl-3,4-bis-pentanoyloxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;trifluoro-acetate; Tetradecanoic acid(2R,3S,4R)-5-((S)-4-amino-2-oxo-2H-pyrimidin-1-yl)-2-azido-3-dihydroxy-tetrahydro-furan-2-ylmethylester;(S)-1-((3R,4S,5R)-5-azido-3,4-bis-butyryloxy-5-hydroxymethyl-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;trifluoro-acetate; and,(S)-1-((3R,4S,5R)-5-Azido-5-decyloxycarbonyloxymethyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-2-oxo-1,2-dihydro-pyrimidin-4-yl-ammonium;trifluoro-acetate.
 15. A method for treating diseases mediated by theHepatitis C Virus (HCV) virus comprising administering to a mammal inneed thereof, a therapeutically effective quantity of a compound offormula I

wherein: R¹ and R² are independently selected from the group consistingof hydrogen, COR⁵, C(═O)OR⁵, C(═O)SR⁵, C(═O)NHR⁵ and COCH(R⁶)NHR⁷; R³and R⁴ are independently selected from the group consisting of hydrogen,COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; or, R³ and R⁴ taken togetherare selected from the group consisting of CH₂, C(CH₃)₂ and CHPh; R⁵ isindependently selected from the group consisting of C₁₋₁₈ unbranched orbranched alkyl, C₁₋₁₈ unbranched or branched alkenyl, C₁₋₁₈ unbranchedor branched alkynyl, C₁₋₁₈ lower haloalkyl, C₃₋₈ cycloalkyl, alkylsubstituted C₃₋₈ cycloalkyl, phenyl optionally substituted with one tothree substituents independently selected from the group consisting ofhalo, lower alkyl, lower alkoxy, lower thioalkyl, lower alkyl sulfinyl,lower alkyl sulfonyl, nitro, cyano, CH₂Ph wherein in phenyl ring isoptionally substituted as described above, and CH₂OPh wherein in phenylring is optionally substituted as described above; R⁶ is independentlyselected from the group consisting of the side chains of naturallyoccurring amino acids and C₁₋₅ unbranched or branched alkyl; R⁷ isselected from the group consisting of hydrogen, R⁵OCO; or, R⁶ and R⁷taken together are (CH₂)₃; and, hydrates, solvates, clathrates and acidaddition salts thereof; with the proviso that at least one of R¹, R²,R³, or R⁴ is other than hydrogen.
 16. The method of claim 15 wherein R¹,R², R³, and R⁴ are each independently COR⁵, C(═O)OR⁵, C(═O)SR⁵ and R⁵ isindependently selected from the group consisting of C₁₋₁₈ unbranched orbranched lower alkyl, C₃₋₈ cycloalkyl, phenyl and CH₂OPh.
 17. The methodof claim 16 wherein R¹, R², R³, and R⁴ are each independently COR⁵ andR⁵ is independently selected from the group consisting of C₁₋₁₈unbranched or branched lower alkyl, C₃₋₈ cycloalkyl, phenyl and CH₂OPh.18. The method of claim 15 wherein R¹ is COR⁵, C(═O)OR⁵, C(═O)SR⁵ orCOCH(R⁶)NHR⁷ and R², R³ and R⁴ are hydrogen.
 19. The method of claim 18wherein R⁵ is selected from a group consisting of C₁₋₁₈ unbranched orbranched lower alkyl, C₃₋₈ cycloalkyl, phenyl and CH₂OPh, or R⁶ isselected from the group consisting of C₁₋₅ unbranched or branched alkyland the side chain of a naturally occurring amino acid and R⁷ ishydrogen.
 20. The method of claim 15 wherein R² is selected from thegroup consisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵, and COCH(R⁶)NHR⁷, R¹, R³and R⁴ are hydrogen.
 21. The method of claim 20 wherein R⁵ is selectedfrom the group consisting of is C₁₋₁₈ unbranched or branched alkyl, C₃₋₈cycloalkyl or phenyl or, R⁶ is C₁₋₅ unbranched or branched alkyl or theside chain of a naturally occurring amino acid.
 22. The method accordingto claim 20 wherein R² is COCH(R⁶)NH₂ and R⁶ is selected from the groupconsisting of C₁₋₅ unbranched or branched alkyl or CH₂Ph.
 23. The methodof claim 15 wherein R³ and R⁴ both are hydrogen.
 24. The method of claim15 wherein R¹ is hydrogen and R²,R³ and R⁴ are independently selectedfrom the group consisting of COR⁵, C(═O)OR⁵, C(═O)SR5.
 25. The method ofclaim 15 wherein R¹ is hydrogen, R² is selected from the groupconsisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷, and R³ and R⁴taken together are selected from the group consisting of CH₂, C(CH₃)₂and CHPh.
 26. The method of claim 15 wherein R¹ and R² are hydrogen andR³ and R⁴ are independently selected from the group consisting of COR⁵,C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷ wherein R⁷ is hydrogen.
 27. Themethod of claim 15 wherein R¹ and R² are selected from the groupconsisting of COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷,and R³ and R⁴taken together are selected from the group consisting of CH₂, C(CH₃)₂and CHPh.
 28. The method of claim 15 wherein the compound is deliveredin a dose of between 1 and 100 mg/kg of body weight of the patient perday.
 29. The method of claim 15 wherein the mammal is a human.
 30. Themethod of claim 15 further comprising administering at least one immunesystem modulator and/or at least one antiviral agent that inhibitsreplication of HCV.
 31. The method of claim 30 further comprisingadministering an immune system modulator.
 32. The method of claim 31wherein the immune system modulator is an interferon, interleukin, tumornecrosis factor or colony stimulating factor or an anti-inflammatoryagent.
 33. The method of claim 32 wherein the immune system modulator isan interferon or chemically derivatized interferon.
 34. The method ofclaim 33 wherein the immune system modulator is interferon-α orchemically derivatized interferon-α.
 35. The method of claim 30 furthercomprising administering at least one other antiviral agent.
 36. Themethod of claim 35 where the antiviral compound is selected from thegroup consisting of an HCV protease inhibitor, another HCV polymeraseinhibitor, an HCV helicase inhibitor, an HCV primase inhibitor and anHCV fusion inhibitor.
 37. A pharmaceutical composition comprising atherapeutically effective quantity of a compound of formula I

wherein: R¹ and R² are independently selected from the group consistingof hydrogen, COR⁵, C(═O)OR⁵, C(═O)SR⁵, C(═O)NHR⁵ and COCH(R⁶)NHR⁷; R³and R⁴ are independently selected from the group consisting of hydrogen,COR⁵, C(═O)OR⁵, C(═O)SR⁵ and COCH(R⁶)NHR⁷; or, R³ and R⁴ taken togetherare selected from the group consisting of CH₂, C(CH₃)₂ and CHPh; R⁵ isindependently selected from the group consisting of C₁₋₈ unbranched orbranched alkyl, C₁₋₁₈ unbranched or branched alkenyl, C₁₋₁₈ unbranchedor branched alkynyl, C₁₋₁₈ lower haloalkyl, C₃₋₈ cycloalkyl, alkylsubstituted C₃₋₈ cycloalkyl, phenyl optionally substituted with one tothree substituents independently selected from the group consisting ofhalo, lower alkyl, lower alkoxy, lower thioalkyl, lower alkyl sulfinyl,lower alkyl sulfonyl, nitro, cyano, CH₂Ph wherein in phenyl ring isoptionally substituted as described above, and CH₂OPh wherein in phenylring is optionally substituted as described above; R⁶ is independentlyselected from the group consisting of the side chains of naturallyoccurring amino acids and C₁₋₅ unbranched or branched alkyl; R⁷ isselected from the group consisting of hydrogen, R⁵OCO; or, R⁶ and R⁷taken together are (CH₂)₃; and, hydrates, solvates, clathrates and acidaddition salts thereof; in combination with one or more pharmaceuticallyacceptable carriers and excipients, with the proviso that at least oneof R¹, R², R³, or R⁴ is other than hydrogen.
 38. A process forconverting an N-acyl cytidine compound IVa to a cytidine compound IVb byselective cleavage of an N-acyl moiety from IVa wherein:

R is independently selected from the group consisting of hydrogen, COR⁵,C(═O)OR⁵, C(═O)SR⁵, C(═O)NHR⁵ and COCH(R⁶)NHR⁷; R⁵ is independentlyselected from the group consisting of C₁₋₁₈ unbranched or branchedalkyl, C₁₋₁₈ unbranched or branched alkenyl, C₁₋₁₈ unbranched orbranched alkynyl, C₁₋₁₈ lower haloalkyl, C₃₋₈ cycloalkyl, alkylsubstituted C₃₋₈ cycloalkyl, phenyl optionally substituted with one tothree substituents independently selected from the group consisting ofhalo, lower alkyl, lower alkoxy, lower thioalkyl, lower alkyl sulfinyl,lower alkyl sulfonyl, nitro, cyano, CH₂Ph wherein in phenyl ring isoptionally substituted as described above, and CH₂OPh wherein in phenylring is optionally substituted as described above; R⁶ is independentlyselected from the group consisting of the side chains of naturallyoccurring amino acids and C₁₋₅ unbranched or branched alkyl; R⁷ isselected from the group consisting of hydrogen, R⁵OCO; or, R⁶ and R⁷together are (CH₂)₃; said process comprising contacting a solution ofsaid N-acyl pyrimidine nucleoside with ZnBr₂ in a protic solvent R^(b)OHwherein R^(a) is hydrogen or C₁₋₄ alkyl.
 39. A process according toclaim 38 wherein said protic solvent is methanol.